CYPRESS FM33256B

FM33256B
3V Integrated Processor Companion with F-RAM
Features
High Integration Device Replaces Multiple Parts
• Serial Nonvolatile Memory
• Real-time Clock (RTC) with Alarm
• Low VDD Detection Drives Reset
• Watchdog Window Timer
• Early Power-Fail Warning/NMI
• 16-bit Nonvolatile Event Counter
• Serial Number with Write-lock for Security
Ferroelectric Nonvolatile RAM
• 256Kb F-RAM
• High Endurance 100 Trillion (1014) Read/Writes
• 38 year Data Retention (+75°C)
• NoDelay™ Writes
Real-time Clock/Calendar
• Backup Current at 2V, 1.15 µA (max.) at +25C
• Seconds through Centuries in BCD format
• Tracks Leap Years through 2099
• Uses Standard 32.768 kHz Crystal
• Software Calibration
• Supports Battery or Capacitor Backup
Description
The FM33256B device integrates F-RAM memory
with the most commonly needed functions for
processor-based systems. Major features include
nonvolatile memory, real-time clock, low-VDD reset,
watchdog timer, nonvolatile event counter, lockable
64-bit serial number area, and general purpose
comparator that can be used for a power-fail (NMI)
interrupt or other purpose. The device operate from
2.7 to 3.6V.
The FM33256B provides 256Kb memory capacity of
nonvolatile F-RAM. Fast write speed and unlimited
endurance allow the memory to serve as extra RAM
or conventional nonvolatile storage. This memory is
truly nonvolatile rather than battery backed.
The real-time clock (RTC) provides time and date
information in BCD format. It can be permanently
powered from external backup voltage source, either
a battery or a capacitor. The timekeeper uses a
common external 32.768 kHz crystal and provides a
calibration mode that allows software adjustment of
timekeeping accuracy.
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Processor Companion
• Active-low Reset Output for VDD and Watchdog
• Programmable Low-VDD Reset Thresholds
• Manual Reset Filtered and Debounced
• Programmable Watchdog Window Timer
• Nonvolatile Event Counter Tracks System
Intrusions or other Events
• Comparator for Power-Fail Interrupt or Other Use
• 64-bit Programmable Serial Number with Lock
Fast SPI Interface
• Up to 16 MHz Maximum Bus Frequency
• RTC, Supervisor Controlled via SPI Interface
• SPI Mode 0 & 3 (CPOL, CPHA=0,0 & 1,1)
Easy to Use Configuration
• Operates from 2.7 to 3.6V
• Small Footprint “Green” 14-pin SOIC (-G)
• Low Operating Current
• -40°C to +85°C Operation
• Underwriters Laboratory (UL) Recognized
The processor companion includes commonly needed
CPU support functions. Supervisory functions
include a reset output signal controlled by either a
low VDD condition or a watchdog timeout. /RST goes
active when VDD drops below a programmable
threshold and remains active for 100 ms (max.) after
VDD rises above the trip point. A programmable
watchdog timer runs from 60 ms to 1.8 seconds. The
timer may also be programmed for a delayed start,
which functions as a window timer. The watchdog
timer is optional, but if enabled it will assert the reset
signal for 100 ms if not restarted by the host within
the time window. A flag-bit indicates the source of
the reset.
A comparator on PFI compares an external input pin
to the onboard 1.5V reference. This is useful for
generating a power-fail interrupt (NMI) but can be
used for any purpose. The family also includes a
programmable 64-bit serial number that can be
locked making it unalterable. Additionally it offers an
event counter that tracks the number of rising or
falling edges detected on a dedicated input pin. The
counter can be programmed to be non-volatile under
VDD power or battery-backed using only VBAK. If
VBAK is connected to a battery or capacitor, then
events will be counted even in the absence of VDD.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 1 of 28
FM33256B SPI Companion w/ FRAM
Pin Configuration
CS
1
14
VDD
SO
2
13
ACS
CNT
3
12
SCK
VBAK
4
11
SI
X2
5
10
PFO
X1
6
9
RST
VSS
7
8
PFI
Pin Name
/CS
SCK
SI
SO
PFI
PFO
CNT
ACS
/RST
X1, X2
VDD
VBAK
VSS
Function
Chip Select
Serial Clock
Serial Data Input
Serial Data Output
Power Fail Input
Power Fail Output (NMI)
Event Counter Input
Alarm/Calibration/SqWave
Reset Input/Output
External Crystal Connections
(optional)
Supply Voltage
Battery-Backup Supply
Ground
Pin Descriptions
Pin Name
/CS
Type
Input
SCK
Input
SI
Input
SO
Output
CNT
Input
ACS
Output
X1, X2
I/O
/RST
I/O
PFI
Input
PFO
Output
VBAK
Supply
VDD
VSS
Supply
Supply
Pin Description
Chip Select: This active low input activates the device. When high, the device enters lowpower standby mode, ignores the SCK and SI inputs, and the SO output is tri-stated.
When low, the device internally activates the SCK signal. A falling edge on /CS must
occur prior to every op-code.
Serial Clock: All I/O activity is synchronized to the serial clock. Inputs are latched on the
rising edge and outputs occur on the falling edge. Since the device is static, the clock
frequency may be any value between 0 and 16 MHz and may be interrupted at any time.
Serial Input: All data is input to the device on this pin. The pin is sampled on the rising
edge of SCK and is ignored at other times. It should always be driven to a valid logic level
to meet IDD specifications. The SI pin may be connected to SO for a single pin data
interface.
Serial Output: This is the data output pin. It is driven during a read and remains tri-stated
at all other times. Data transitions are driven on the falling edge of the serial clock. The
SO pin may be connected to SI for a single pin data interface.
Event Counter Input: This input increments the counter when an edge is detected on this
pin. The polarity is programmable and the counter value is nonvolatile or battery-backed,
depending on the mode. This pin should be tied to ground if unused.
Alarm/Calibration/SquareWave: This is an open-drain output that requires an external
pullup resistor. In normal operation, this pin acts as the active-low alarm output. In
Calibration mode, a 512 Hz square-wave is driven out. In SquareWave mode, the user
may select a frequency of 1, 512, 4096, or 32768 Hz to be used as a continuous output.
The SquareWave mode is entered by clearing the AL/SW and CAL bits in register 18h.
32.768 kHz crystal connection (see Crystal Type section for suggestions). See AN407
app. note for details on how to connect external oscillator.
Reset: This active-low output is open drain with weak pull-up. It is also an input when
used as a manual reset. This pin should be left floating if unused.
Early Power-fail Input: Typically connected to an unregulated power supply to detect an
early power failure. This pin must be tied to ground if unused.
Early Power-fail Output: This pin is the early power-fail output and is typically used to
drive a microcontroller NMI pin. PFO drives low when the PFI voltage is <1.5V.
Backup supply voltage: A 3V battery or a large value capacitor. If no backup supply is
used, this pin should be tied to VSS and the VBC bit should be cleared. The trickle charger
is UL recognized and ensures no excessive current when using a lithium battery.
Supply Voltage.
Ground
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 2 of 28
FM33256B SPI Companion w/ FRAM
CS
SPI
Interface
SCK
FRAM
Array
SI
SO
LockOut
Watchdog
Special
Function
Registers
LV Detect
S/N
Manual Reset
RST
PFI
-
RTC
X2
1.5V
Event
Counter
CNT
VSW
X1
RTC Cal.
+
PFO
RTC Registers
Alarm
-
Alarm
+
ACS
512Hz/SqW
VDD
Switched Power
VBAK
Battery Backed
Nonvolatile
NV/BB User Programmable
Figure 1. Block Diagram
Ordering Information
Base
Configuration
Memory
Size
Operating
Voltage
Max. Clock
Freq.
Reset Thresholds
FM33256B
256Kb
2.7-3.6V
16 MHz
2.6V, 2.75, 2.9, 3.0V
FM33256B-G
FM33256B
256Kb
2.7-3.6V
16 MHz
2.6V, 2.75, 2.9, 3.0V
FM33256B-GTR (tape&reel)
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ordering Part Number
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 3 of 28
FM33256B SPI Companion w/ FRAM
Overview
Processor Companion
The FM33256B device combines a serial nonvolatile
RAM with a real-time clock (RTC) and a processor
companion. The companion is a highly integrated
peripheral including a processor supervisor, analog
comparator, a nonvolatile counter, and a serial
number.
The
FM33256B
integrates
these
complementary but distinct functions under a
common interface in a single package. The product is
organized as two logical devices. The first is a
memory and the second is the companion which
includes all the remaining functions. From the system
perspective they appear to be two separate devices
with unique op-codes on the serial bus.
In addition to nonvolatile RAM, the FM33256B
incorporates a real-time clock with alarm and highly
integrated processor companion. The companion
includes a low-VDD reset, a programmable watchdog
timer, a 16-bit nonvolatile event counter, a
comparator for early power-fail detection or other
purposes, and a 64-bit serial number.
The memory is organized as a standalone nonvolatile
SPI memory using standard op-codes. The real-time
clock and supervisor functions are accessed under
their own op-codes. The clock and supervisor
functions are controlled by 30 special function
registers. The RTC/alarm and some control registers
are maintained by the power source on the VBAK
pin, allowing them to operate from battery or backup
capacitor power when VDD drops below a set
threshold. Each functional block is described below.
Memory Operation
The FM33256B is available with 256Kb of memory.
The device uses two-byte addressing for the memory
portion of the chip. This makes the device software
compatible with its standalone memory counterparts,
such as the FM25W256.
Memory is organized in bytes. The 256Kb memory is
32,768 x 8. The memory is based on F-RAM
technology. Therefore it can be treated as RAM and
is read or written at the speed of the SPI bus with no
delays for write operations. It also offers effectively
unlimited write endurance unlike other nonvolatile
memory technologies. The SPI protocol is described
on page 18.
The memory array can be write-protected by
software. Two bits (BP0, BP1) in the Status Register
control the protection setting. Based on the setting,
the protected addresses cannot be written. The Status
Register & Write Protection is described in more
detail on page 20.
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Processor Supervisor
Supervisors provide a host processor two basic
functions: Detection of power supply fault conditions
and a watchdog timer to escape a software lockup
condition. The FM33256B has a reset pin (/RST) to
drive a processor reset input during power faults,
power-up, and software lockups. It is an open drain
output with a weak internal pull-up to VDD. This
allows other reset sources to be wire-OR’d to the
/RST pin. When VDD is above the programmed trip
point, /RST output is pulled weakly to VDD. If VDD
drops below the reset trip point voltage level (VTP),
the /RST pin will be driven low. It will remain low
until VDD falls too low for circuit operation which is
the VRST level. When VDD rises again above VTP,
/RST continues to drive low for at least 50 ms (tRPU)
to ensure a robust system reset at a reliable VDD level.
After tRPU has been met, the /RST pin will return to
the weak high state. While /RST is asserted, serial
bus activity is locked out even if a transaction
occurred as VDD dropped below VTP. A memory
operation started while VDD is above VTP will be
completed internally.
Table 1 below shows how bits VTP(1:0) control the
trip point of the low-VDD reset. They are located in
register 18h, bits 0 and 1. The reset pin will drive
low when VDD is below the selected VTP voltage, and
the SPI interface and F-RAM array will be locked
out. Figure 2 illustrates the reset operation in
response to a low VDD.
VTP Setting
2.6V
2.75V
2.9V
3.0V
VTP1
0
0
1
1
VTP0
0
1
0
1
Table 1.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 4 of 28
FM33256B SPI Companion w/ FRAM
VDD
tRPU
VTP
RST
Figure 2. Low VDD Reset
A watchdog timer can also be used to drive an active
reset signal. The watchdog is a free-running
programmable timer. The timeout period can be
software programmed from 60 ms to 1.8 seconds in
60 ms increments via a 5-bit nonvolatile setting
(register 0Ch).
WR3-0 = 1010b
to restart
100 ms
clock
Timebase
Down Counter
/RST
Watchdog
Timer Settings
WDE
Figure 3. Watchdog Timer
The watchdog also incorporates a window timer
feature that allows a delayed start. The starting time
and ending time defines the window and each may be
set independently. The starting time has 25 ms
resolution and 0 ms to 775 ms range.
Watchdog
Restart
Start
Time
End
Time
timer as described above. This assures that the full
timeout is provided immediately after enabling. The
watchdog is disabled when VDD drops below VTP.
Note setting the EndTime timeout setting to all
zeroes (00000b) disables the timer to save power.
The listing below summarizes the watchdog bits.
Watchdog StartTime
Watchdog EndTime
Watchdog Enable
Watchdog Restart
Watchdog Flags
WDST4-0
WDET4-0
WDE
WR3-0
EWDF,
LWDF
0Bh, bits 4-0
0Ch, bits 4-0
0Ch, bit 7
0Ah, bits 3-0
09h, bit 7
09h, bit 6
The programmed StartTime value is a guaranteed
maximum time while the EndTime value is a
guaranteed minimum time, and both vary with
temperature and VDD voltage. The watchdog has two
additional controls associated with its operation. The
nonvolatile enable bit WDE allows the /RST to go
active if the watchdog reaches the timeout without
being restarted. If a reset occurs, the timer will restart
on the rising edge of the reset pulse. If WDE is not
enabled, the watchdog timer still runs but has no
effect on /RST. The second control is a nibble that
restarts the timer, thus preventing a reset. The timer
should be restarted after changing the timeout value.
This procedure must be followed to properly load the
watchdog registers:
1.
2.
3.
Address
Write the StartTime value
0Bh
Write the EndTime value and WDE=1 0Ch
Issue a Restart command
0Ah
The restart command in step 3 must be issued before
tDOG2, which was programmed in step 2. The window
timer starts counting when the restart command is
issued.
Window
RST
100 ms (max)
Figure 4. Window Timer
The watchdog EndTime value is located in register
0Ch, bits 4-0, the watchdog enable is bit 7. The
watchdog is restarted by writing the pattern 1010b to
the lower nibble of register 0Ah. Writing the correct
pattern will also cause the timer to load new timeout
values. Writing other patterns to this address will not
affect its operation. Note the watchdog timer is freerunning. Prior to enabling it, users should restart the
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Manual Reset
The /RST is a bi-directional signal allowing the
FM33256B to filter and de-bounce a manual reset
switch. The /RST input detects an external low
condition and responds by driving the /RST signal
low for 100 ms (max.). This effectively filters and debounces a reset switch. After this timeout (tRPU), the
user may continue pulling down on the /RST pin, but
SPI commands will not be locked out.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 5 of 28
FM33256B SPI Companion w/ FRAM
MCU
RST
FM33256B
Regulator
VDD
Reset
Switch
Switch
Behavior
FM33256B
RST
FM33256B
drives
100 ms (max.)
To MCU
NMI input
PFO
+
-
1.5V ref
Figure 5. Manual Reset
Note the internal weak pull-up eliminates the need
for additional external components.
Reset Flags
In case of a reset condition, a flag bit will be set to
indicate the source of the reset. A low-VDD reset is
indicated by the POR bit, register 09h bit 5. There are
two watchdog reset flags - one for an early fault
(EWDF) and the other for a late fault (LWDF),
located in register 09h bits 7 and 6. A manual reset
will result in no flag being set, so the absence of a
flag is a manual reset. Note that the bits are set in
response to reset sources but they must be cleared by
the user. It is possible to read the register and have
both sources indicated if both have occurred since the
user cleared them.
Power Fail Comparator
An analog comparator compares the PFI input pin to
an onboard 1.5V reference. When the PFI input
voltage drops below this threshold, the comparator
will drive the PFO pin to a low state. The comparator
has 100 mV of hysteresis (rising voltage only) to
reduce noise sensitivity. The most common
application of this comparator is to create an early
warning power fail interrupt (NMI). This can be
accomplished by connecting the PFI pin to an
upstream power supply via a resistor divider. An
application circuit is shown below. The comparator is
a general purpose device and its application is not
limited to the NMI function.
Figure 6. Comparator as a Power-Fail Warning
If the power-fail comparator is not used, the PFI pin
should be tied to either VDD or VSS. Note that the
PFO output will drive to VDD or VSS as well.
Event Counter
The FM33256B offers the user a nonvolatile 16-bit
event counter. The input pin CNT has a
programmable edge detector. The CNT pin clocks the
counter. The counter is located in registers 0E-0Fh.
When the programmed edge polarity occurs, the
counter will increment its count value. The register
value is read by setting the RC bit (register 0Dh, bit
3) to 1. This takes a snapshot of the counter byte
allowing a stable value even if a count occurs during
the read. The register value can be written by first
setting the WC bit (register 0Dh, bit 2) to 1. The user
then may clear or preset the counter by writing to
registers 0E-0Fh. Counts are blocked when the WC
bit is set, so the user must clear the bit to allow
counts.
The counter polarity control bit is CP, register 0Dh
bit 0. When CP is 0, the counter increments on a
falling edge of CNT, and when CP is set to 1, the
counter increments on a rising edge of CNT. The
polarity bit CP is nonvolatile.
CP
16-bit Counter
CNT
Figure 7. Event Counter
The counter does not wrap back to zero when it
reaches the limit of 65,535 (FFFFh). Care must be
taken prior to the rollover, and a subsequent counter
reset operation must occur to continue counting.
There is also a control bit that allows the user to
define the counter as nonvolatile or battery-backed.
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 6 of 28
FM33256B SPI Companion w/ FRAM
The counter is nonvolatile when the NVC bit
(register 0Dh, bit 7) is logic 1 and battery-backed
when the NVC bit is logic 0. Setting the counter
mode to battery-backed allows counter operation
under VBAK (as well as VDD) power. The lowest
operating voltage for battery-backed mode is 2.0V.
When set to “nonvolatile” mode, the counter operates
only when VDD is applied and is above the VTP
voltage.
The event counter may be programmed to detect a
tamper event, such as the system’s case or access
door being opened. A normally closed switch is tied
to the CNT pin and the other contact to the case
chassis, usually ground. The typical solution uses a
pullup resistor on the CNT pin and will continuously
draw battery current. The FM33256B chip allows the
user to invoke a polled mode, which occasionally
samples the pin in order to minimize battery drain. It
internally tries to pull the CNT pin up and if open
circuit will be pulled up to a VIH level, which will trip
the edge detector and increment the event counter
value. Setting the POLL bit (register 0Dh, bit 1)
places the CNT pin into this mode. This mode allows
the event counter to detect a rising edge tamper event
but the user is restricted to operating in batterybacked mode (NVC=0) and using rising edge
detection (CP=1). The CNT pin is polled once every
125ms. The additional average IBAK current is less
than 20nA. The polling timer circuit operates from
the RTC, so the oscillator must be enabled for this to
function properly.
Vbak
FM33256B
< 100pF
CNT
125ms
Figure 8. Polled Mode on CNT pin Detects Tamper
In the polled mode, the internal pullup circuit can
source a limited amount of current. The maximum
capacitance (switch open circuit) allowed on the CNT
pin is 100pF.
Serial Number
A memory location to write a 64-bit serial number is
provided. It is a writeable nonvolatile memory block
that can be locked by the user once the serial number
is set. The 8 bytes of data and the lock bit are all
accessed via unique op-codes for the RTC and
Processor Companion registers. Therefore the serial
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
number area is separate and distinct from the memory
array. The serial number registers can be written an
unlimited number of times, so these locations are
general purpose memory. However once the lock bit
is set, the values cannot be altered and the lock
cannot be removed. Once locked the serial number
registers can still be read by the system.
The serial number is located in registers 10h to 17h.
The lock bit is SNL, register 18h bit 7. Setting the
SNL bit to a 1 disables writes to the serial number
registers, and the SNL bit cannot be cleared.
Alarm
The alarm function compares user-programmed
values to the corresponding time/date values and
operates under VDD or VBAK power. When a match
occurs, an alarm event occurs. The alarm drives an
internal flag AF (register 00h, bit 6) and may drive
the ACS pin, if desired, by setting the AL/SW bit
(register 18h, bit 6) in the Companion Control
register. The alarm condition is cleared by writing a
‘0’ to the AF bit.
There are five alarm match fields. They are Month,
Date, Hours, Minutes, and Seconds. Each of these
fields also has a Match bit that is used to determine if
the field is used in the alarm match logic. Setting the
Match bit to ‘0’ indicates that the corresponding field
will be used in the match process.
Depending on the Match bits, the alarm can occur as
specifically as one particular second on one day of
the month, or as frequently as once per second
continuously. The MSB of each Alarm register is a
Match bit. Examples of the Match bit settings are
shown in Table 3. Selecting none of the match bits
(all ‘1’s) indicates that no match is required. The
alarm occurs every second. Setting the match select
bit for seconds to ‘0’ causes the logic to match the
seconds alarm value to the current time of day. Since
a match will occur for only one value per minute, the
alarm occurs once per minute. Likewise setting the
seconds and minutes match select bits causes an
exact match of these values. Thus, an alarm will
occur once per hour. Setting seconds, minutes, and
hours causes a match once per day. Lastly, selecting
all match-values causes an exact time and date match.
Selecting other bit combinations will not produce
meaningful results, however the alarm circuit will
follow the functions described.
There are two ways a user can detect an alarm event,
by reading the AF flag or monitoring the ACS pin.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 7 of 28
FM33256B SPI Companion w/ FRAM
The interrupt pin on the host processor may be used
to detect an alarm event. The AF flag in register 00h
(bit 6) will indicate that a time/date match has
occurred. The AF flag will be set to ‘1’ when a match
occurs. The AEN bit must be set to enable the AF
flag on alarm matches. The flag and ACS pin will
remain in this state until the AF bit is cleared by
writing it to a ‘0’. Clearing the AEN bit will prevent
further matches from setting AF but will not
automatically clear the AF flag.
The RTC alarm is integrated into the special function
registers and shares its output pin with the 512Hz
calibration and square wave outputs. When the RTC
calibration mode is invoked by setting the CAL bit
(register 00h, bit 2), the ACS output pin will be
driven with a 512 Hz square wave and the alarm will
continue to operate. Since most users only invoke the
calibration mode during production this should have
no impact on the otherwise normal operation of the
alarm.
The ACS output may also be used to drive the system
with a frequency other than 512 Hz. The AL/SW bit
(register 18h, bit 6) must be ‘0’. A user-selectable
frequency is provided by F0 and F1 (register 18h, bits
4 and 5). The other frequencies are 1, 4096, and
32768 Hz. If a continuous frequency output is
enabled with CAL mode, the alarm function will not
be available.
Following is a summary table that shows the
relationship between register control settings and the
state of the ACS pin.
Table 2. State of Register Bit
State of Register Bit
Function of
ACS pin
CAL AEN AL/SW
0
1
1
/Alarm
0
X
0
Sq Wave out
1
X
X
512 Hz out
0
0
1
Hi-Z
Table 3. Alarm Match Bit Examples
Seconds
Minutes
Hours
Date
Months
1
1
1
1
1
Alarm condition
No match required = alarm 1/second
0
1
1
1
1
Alarm when seconds match = alarm 1/minute
0
0
1
1
1
Alarm when seconds, minutes match = alarm 1/hour
0
0
0
1
1
Alarm when seconds, minutes, hours match = alarm 1/date
0
0
0
0
1
Alarm when seconds, minutes, hours, date match = alarm 1/month
Real-time Clock Operation
The real-time clock (RTC) is a timekeeping device
that can be capacitor- or battery-backed for
permanently-powered operation. It offers a software
calibration feature that allows high accuracy.
The RTC consists of an oscillator, clock divider, and
a register system for user access. It divides down the
32.768 kHz time-base and provides a minimum
resolution of seconds (1Hz). Static registers provide
the user with read/write access to the time values. It
includes registers for seconds, minutes, hours, dayof-the-week, date, months, and years. A block
diagram shown in Figure 9 illustrates the RTC
function.
The user registers are synchronized with the
timekeeper core using R and W bits in register 00h.
The R bit is used to read the time. Changing the R bit
from 0 to 1 transfers timekeeping information from
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
the core into the user registers 02-08h that can be
read by the user. If a timekeeper update is pending
when R is set, then the core will be updated prior to
loading the user registers. The user registers are
frozen and will not be updated again until the R bit is
cleared to a ‘0’.
The W bit is used to write new time/date values.
Setting the W bit to a ‘1’ stops the RTC and allows
the timekeeping core to be written with new data.
Clearing it to ‘0’ causes the RTC to start running
based on the new values loaded in the timekeeper
core. The RTC may be synchronized to another clock
source. On the 8th clock of the write to register 00h
(W=0), the RTC starts counting with a timebase that
has been reset to zero milliseconds.
Note: Users should be certain not to load invalid
values, such as FFh, to the timekeeping registers.
Updates to the timekeeping core occur continuously
except when locked.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 8 of 28
FM33256B SPI Companion w/ FRAM
512 Hz or
SW out
/OSCEN
32.768 kHz
crystal
CF
Years
8 bits
Clock
Divider
Oscillator
Months
5 bits
Date
6 bits
Hours
6 bits
1 Hz
Minutes
7 bits
W
Update
Logic
Seconds
7 bits
Days
3 bits
R
User Registers
Figure 9. Real-time Clock Core Block Diagram
Backup Power
The real-time clock/calendar is intended to be
permanently powered. When the primary system
power fails, the voltage on the VDD pin will drop.
When VDD is less 2.5V, the RTC (and event counters)
will switch to the backup power supply on VBAK. The
clock operates at extremely low current in order to
maximize battery or capacitor life. However, an
advantage of combining a clock function with FRAM
memory is that data is not lost regardless of the
backup power source.
Figure 10. IBAK vs. VBAK Voltage
The IBAK current varies with temperature and voltage
(see DC parametric table). Figure 10 shows IBAK as a
function of VBAK. These curves are useful for
calculating backup time when a capacitor is used as
the VBAK source.
The minimum VBAK voltage varies linearly with
temperature. The user can expect the minimum VBAK
voltage to be 1.23V at +85°C and 1.90V at -40°C.
The tested limit is 1.55V at +25°C.
Figure 11. VBAK (min.) vs Temperature
Note: The minimum VBAK voltage has been
characterized at -40°C and +85°C but is not
100% tested.
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 9 of 28
FM33256B SPI Companion w/ FRAM
Trickle Charger
To facilitate capacitor backup, the VBAK pin can
optionally provide a trickle charge current. When the
VBC bit (register 18h bit 3) is set to a ‘1’, the VBAK
pin will source approximately 80 µA until VBAK
reaches VDD. This charges the capacitor to VDD
without an external diode and resistor charger.
There is a Fast Charge mode which is enabled by the
FC bit (register 18h, bit 2). In this mode the trickle
charger current is set to approximately 1 mA,
allowing a large backup capacitor to charge more
quickly.
• In the case where no battery is used, the VBAK
pin should be tied to VSS and VBC bit cleared.
 Note: systems using lithium batteries should clear
the VBC bit to 0 to prevent battery charging. The
VBAK circuitry includes an internal 1 KΩ series
resistor as a safety element. The trickle charger is UL
Recognized.
Calibration
When the CAL bit in register 00h is set to a ‘1’, the
clock enters calibration mode. The FM33256B
employs a digital method for calibrating the crystal
oscillator frequency. The digital calibration scheme
applies a digital correction to the RTC counters based
on the calibration settings, CALS and CAL.4-0. In
calibration mode (CAL=1), the ACS pin is driven
with a 512 Hz (nominal) square wave and the alarm
is temporarily unavailable. Any measured deviation
The calibration setting is stored in F-RAM so it is not
lost should the backup source fail. It is accessed with
bits CAL.4-0 in register 01h. This value only can be
written when the CAL bit is set to a 1. To exit the
calibration mode, the user must clear the CAL bit to a
logic 0. When the CAL bit is 0, the ACS pin will
revert to the function according to Table 2.
Crystal Type
The crystal oscillator is designed to use a 12.5pF
crystal without the need for external components,
such as loading capacitors. The FM33256B device
has built-in loading capacitors that match the crystal.
If a 32.768kHz crystal is not used, an external
oscillator may be connected to the FM33256B. Refer
to Application Note AN407 for recommendations on
how to implement this.
Layout Recommendations
The X1 and X2 crystal pins employ very high
impedance circuits and the oscillator connected to
these pins can be upset by noise or extra loading. To
reduce RTC clock errors from signal switching noise,
a guard ring should be placed around these pads and
the guard ring grounded. High speed SPI traces
should be routed away from the X1/X2 pads. The X1
and X2 trace lengths should be less than 5 mm. The
use of a ground plane on the backside or inner board
layer is preferred. See layout example. Red is the top
layer, green is the bottom layer.
from 512 Hz translates into a timekeeping error. The
user measures the frequency and writes the
appropriate correction value to the calibration
register. The correction codes are listed in the table
below. For convenience, the table also shows the
frequency error in ppm. Positive ppm errors require a
negative adjustment that removes pulses. Negative
ppm errors require a positive correction that adds
pulses. Positive ppm adjustments have the CALS
(sign) bit set to 1, where as negative ppm adjustments
have CALS = 0. After calibration, the clock will have
a maximum error of ± 2.17 ppm or ± 0.09 minutes
per month at the calibrated temperature.
The user will not be able to see the effect of the
calibration setting on the 512 Hz output. The
addition or subtraction of digital pulses occurs after
the 512 Hz output.
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 10 of 28
FM33256B SPI Companion w/ FRAM
/CS
/CS
SO
SO
CNT
CNT
VBAK
VBAK
X2
X2
X1
X1
VSS
VSS
Layout for Surface Mount Crystal
Layout for Through Hole Crystal
(red = top layer, green = bottom layer)
(red = top layer, green = bottom layer)
Table 4. Digital Calibration Adjustments
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Positive Calibration for slow clocks: Calibration will achieve ± 2.17 PPM after calibration
Measured Frequency Range
Error Range (PPM)
Min
Max
Min
Max
Program Calibration Register to:
512.0000
511.9989
0
2.17
000000
511.9989
511.9967
2.18
6.51
100001
511.9967
511.9944
6.52
10.85
100010
511.9944
511.9922
10.86
15.19
100011
511.9922
511.9900
15.20
19.53
100100
511.9900
511.9878
19.54
23.87
100101
511.9878
511.9856
23.88
28.21
100110
511.9856
511.9833
28.22
32.55
100111
511.9833
511.9811
32.56
36.89
101000
511.9811
511.9789
36.90
41.23
101001
511.9789
511.9767
41.24
45.57
101010
511.9767
511.9744
45.58
49.91
101011
511.9744
511.9722
49.92
54.25
101100
511.9722
511.9700
54.26
58.59
101101
511.9700
511.9678
58.60
62.93
101110
511.9678
511.9656
62.94
67.27
101111
511.9656
511.9633
67.28
71.61
110000
511.9633
511.9611
71.62
75.95
110001
511.9611
511.9589
75.96
80.29
110010
511.9589
511.9567
80.30
84.63
110011
511.9567
511.9544
84.64
88.97
110100
511.9544
511.9522
88.98
93.31
110101
511.9522
511.9500
93.32
97.65
110110
511.9500
511.9478
97.66
101.99
110111
511.9478
511.9456
102.00
106.33
111000
511.9456
511.9433
106.34
110.67
111001
511.9433
511.9411
110.68
115.01
111010
511.9411
511.9389
115.02
119.35
111011
511.9389
511.9367
119.36
123.69
111100
511.9367
511.9344
123.70
128.03
111101
511.9344
511.9322
128.04
132.37
111110
511.9322
511.9300
132.38
136.71
111111
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 11 of 28
FM33256B SPI Companion w/ FRAM
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Negative Calibration for fast clocks: Calibration will achieve ± 2.17 PPM after calibration
Measured Frequency Range
Error Range (PPM)
Min
Max
Min
Max
Program Calibration Register to:
512.0000
512.0011
0
2.17
000000
512.0011
512.0033
2.18
6.51
000001
512.0033
512.0056
6.52
10.85
000010
512.0056
512.0078
10.86
15.19
000011
512.0078
512.0100
15.20
19.53
000100
512.0100
512.0122
19.54
23.87
000101
512.0122
512.0144
23.88
28.21
000110
512.0144
512.0167
28.22
32.55
000111
512.0167
512.0189
32.56
36.89
001000
512.0189
512.0211
36.90
41.23
001001
512.0211
512.0233
41.24
45.57
001010
512.0233
512.0256
45.58
49.91
001011
512.0256
512.0278
49.92
54.25
001100
512.0278
512.0300
54.26
58.59
001101
512.0300
512.0322
58.60
62.93
001110
512.0322
512.0344
62.94
67.27
001111
512.0344
512.0367
67.28
71.61
010000
512.0367
512.0389
71.62
75.95
010001
512.0389
512.0411
75.96
80.29
010010
512.0411
512.0433
80.30
84.63
010011
512.0433
512.0456
84.64
88.97
010100
512.0456
512.0478
88.98
93.31
010101
512.0478
512.0500
93.32
97.65
010110
512.0500
512.0522
97.66
101.99
010111
512.0522
512.0544
102.00
106.33
011000
512.0544
512.0567
106.34
110.67
011001
512.0567
512.0589
110.68
115.01
011010
512.0589
512.0611
115.02
119.35
011011
512.0611
512.0633
119.36
123.69
011100
512.0633
512.0656
123.70
128.03
011101
512.0656
512.0678
128.04
132.37
011110
512.0678
512.0700
132.38
136.71
011111
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 12 of 28
FM33256B SPI Companion w/ FRAM
Register Map
The RTC and processor companion functions are accessed via 30 special function registers, which are mapped to
unique op-codes. The interface protocol is described on page 18. The registers contain timekeeping data, alarm
settings, control bits, and information flags. A description of each register follows the summary table.
Register Map Summary Table
Battery-backed =
Nonvolatile =
Address
1Dh
1Ch
1Bh
1Ah
19h
18h
17h
16h
15h
14h
13h
12h
11h
10h
0Fh
0Eh
0Dh
0Ch
0Bh
0Ah
09h
08h
07h
06h
05h
04h
03h
02h
01h
00h
D7
/Match
/Match
/Match
/Match
/Match
SNL
NVC
WDE
EWDF
0
0
0
0
0
0
/OSCEN
D6
0
0
0
BB/NV User Programmable =
D5
0
D4
10 mo
10 date
Alarm 10 hours
Alarm 10 minutes
Alarm 10 seconds
AL/SW
F1
F0
D3
VBC
Serial Number Byte 7
Serial Number Byte 6
Serial Number Byte 5
Serial Number Byte 4
Serial Number Byte 3
Serial Number Byte 2
Serial Number Byte 1
Serial Number Byte 0
Event Counter Byte 1
Event Counter Byte 0
RC
WDSET4 WDET3
WDST4
WDST3
WR3
LB
-
LWDF
POR
10 years
0
0
10 mo
10 date
0
0
0
0
10 hours
0
10 minutes
10 seconds
CALS
CAL4
AF
CF
AEN
0
CAL3
reserved
D2
D1
Alarm months
Alarm date
Alarm hours
Alarm minutes
Alarm seconds
FC
VTP1
WC
POLL
WDET2
WDET1
WDST2
WDST1
WR2
WR1
years
months
date
day
hours
minutes
seconds
CAL2
CAL1
CAL
W
D0
VTP0
CP
WDET0
WDST0
WR0
-
CAL0
R
Function
Alarm Month
Alarm Date
Alarm Hours
Alarm Minutes
Alarm Seconds
Companion Control
Serial Number 7
Serial Number 6
Serial Number 5
Serial Number 4
Serial Number 3
Serial Number 2
Serial Number 1
Serial Number 0
Event Counter 1
Event Counter 0
Event Counter Control
Watchdog Control
Watchdog Control
Watchdog Restart
Watchdog Flags
Years
Month
Date
Day
Hours
Minutes
Seconds
CAL/Control
RTC/Alarm Control
Range
01-12
01-31
00-23
00-59
00-59
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
00-99
01-12
01-31
01-07
00-23
00-59
00-59
Note: When the device is first powered up and programmed, all timekeeping registers must be written because the batterybacked register values cannot be guaranteed. The table below shows the default values of the non-volatile registers and some of
the battery-backed bits. All other register values should be treated as unknown.
Default Register Values
Address
1Dh
1Ch
1Bh
1Ah
19h
18h
17h
16h
15h
14h
13h
Hex Value
0x81
0x81
0x80
0x80
0x80
0x40
0x00
0x00
0x00
0x00
0x00
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Address
12h
11h
10h
0Fh
0Eh
0Dh
0Ch
0Bh
01h
00h
Hex Value
0x00
0x00
0x00
0x00
0x00
0x01
0x00
0x00
0x00
0x80
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 13 of 28
FM33256B SPI Companion w/ FRAM
Register Description
Address
Description
1Dh
Alarm – Month
D7
D6
D5
D4
D3
D2
D1
D0
M
0
0
10 Month
Month.3
Month.2
Month.1
Month.0
/M
Contains the alarm value for the month and the mask bit to select or deselect the Month value.
Match. Setting this bit to 0 causes the Month value to be used in the alarm match logic. Setting this bit to 1
causes the match circuit to ignore the Month value. Battery-backed, read/write.
1Ch
Alarm – Date
D7
D6
D5
D4
D3
D2
D1
D0
M
0
10 date.1
10 date.0
Date.3
Date.2
Date.1
Date.0
/M
Contains the alarm value for the date and the mask bit to select or deselect the Date value.
Match: Setting this bit to 0 causes the Date value to be used in the alarm match logic. Setting this bit to 1 causes
the match circuit to ignore the Date value. Battery-backed, read/write.
1Bh
Alarm – Hours
D7
D6
D5
D4
D3
D2
D1
D0
M
0
10 hours.1
10 hours.0
Hours.3
Hours2
Hours.1
Hours.0
/M
Contains the alarm value for the hours and the mask bit to select or deselect the Hours value.
Match: Setting this bit to 0 causes the Hours value to be used in the alarm match logic. Setting this bit to 1 causes
the match circuit to ignore the Hours value. Battery-backed, read/write.
1Ah
Alarm – Minutes
D7
D6
D5
D4
D3
D2
D1
D0
M
10 min.2
10 min.1
10 min.0
Min.3
Min.2
Min.1
Min.0
/M
Contains the alarm value for the minutes and the mask bit to select or deselect the Minutes value
Match: Setting this bit to 0 causes the Minutes value to be used in the alarm match logic. Setting this bit to 1
causes the match circuit to ignore the Minutes value. Battery-backed, read/write.
19h
Alarm – Seconds
D7
D6
D5
D4
D3
D2
D1
D0
M
10 sec.2
10 sec.1
10 sec.0
Seconds.3
Seconds.2
Seconds.1
Seconds.0
/M
Contains the alarm value for the seconds and the mask bit to select or deselect the Seconds value.
Match: Setting this bit to 0 causes the Seconds value to be used in the alarm match logic. Setting this bit to 1
causes the match circuit to ignore the Seconds value. Battery-backed, read/write.
18h
Companion Control
SNL
AL/SW
F(1:0)
D7
D6
D5
D4
D3
D2
D1
D0
SNL
AL/SW
F1
F0
VBC
FC
VTP1
VTP0
Serial Number Lock: Setting to a ‘1’ makes registers 10h to 17h and SNL read-only. SNL cannot be cleared once
set to ‘1’. Nonvolatile, read/write.
Alarm/Square Wave Select: When set to ‘1’, the alarm match drives the ACS pin as well as the AF flag. When
set to ‘0’, the selected Square Wave Freq will be driven on the ACS pin, and an alarm match only sets the AF
flag. Nonvolatile, read/write.
Square Wave Freq Select: These bits select the frequency on the ACS pin when the CAL and AL/SW bits are
both ‘0’. Nonvolatile.
Setting
1 Hz
512 Hz
VBC
FC
VTP(1:0)
F(1:0)
00 (default)
01
Setting
4096 Hz
32768Hz
F(1:0)
10
11
VBAK Charger Control: Setting VBC to ‘1’ (and FC=0) causes a 80 µA (1 mA if FC=1) trickle charge current to
be supplied on VBAK. Clearing VBC to ‘0’ disables the charge current. Battery-backed, read/write.
Fast Charge: Setting FC to ‘1’ (and VBC=1) causes a ~1 mA trickle charge current to be supplied on VBAK.
Clearing VBC to ‘0’ disables the charge current. Battery-backed, read/write.
VTP Select. These bits control the reset trip point for the low-VDD reset function. When VDD is below the
selected VTP voltage, the reset pin /RST will drive low and the SPI interface will be locked out. Nonvolatile,
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 14 of 28
FM33256B SPI Companion w/ FRAM
read/write.
Setting
2.60V
2.75V
2.9V
3.0V
17h
16h
15h
14h
13h
12h
11h
10h
VTP(1:0)
00 (factory default)
01
10
11
Serial Number Byte 7
D7
D6
D5
D4
D3
D2
D1
D0
SN.63
SN.62
SN.61
SN.60
SN.59
SN.58
SN.57
SN.56
Serial Number Byte 6
D7
D6
D5
D4
D3
D2
D1
D0
SN.55
SN.54
SN.53
SN.52
SN.51
SN.50
SN.49
SN.48
Serial Number Byte 5
D7
D6
D5
D4
D3
D2
D1
D0
SN.47
SN.46
SN.45
SN.44
SN.43
SN.42
SN.41
SN.40
Serial Number Byte 4
D7
D6
D5
D4
D3
D2
D1
D0
SN.39
SN.38
SN.37
SN.36
SN.35
SN.34
SN.33
SN.32
Serial Number Byte 3
D7
D6
D5
D4
D3
D2
D1
D0
SN.31
SN.30
SN.29
SN.28
SN.27
SN.26
SN.25
SN.24
Serial Number Byte 2
D7
D6
D5
D4
D3
D2
D1
D0
SN.23
SN.22
SN.21
SN.20
SN.19
SN.18
SN.17
SN.16
Serial Number Byte 1
D7
D6
D5
D4
D3
D2
D1
D0
SN.15
SN.14
SN.13
SN.12
SN.11
SN.10
SN.9
SN.8
Serial Number Byte 0
D7
D6
D5
D4
D3
D2
D1
D0
SN.7
SN.6
SN.5
SN.4
SN.3
SN.2
SN.1
SN.0
All serial number bytes are read/write when SNL=0, read-only when SNL=1. Nonvolatile.
0Fh
Event Counter Byte 1
D7
D6
D5
D4
D3
D2
D1
D0
EC.15
EC.14
EC.13
EC.12
EC.11
EC.10
EC.9
EC.8
Event Counter Byte 1. Increments on programmed edge event on CNT input. Nonvolatile when NVC=1,
Battery-backed when NVC=0, read/write.
0Eh
Event Counter Byte 0
D7
D6
D5
D4
D3
D2
D1
D0
EC.7
EC.6
EC.5
EC.4
EC.3
EC.2
EC.1
EC.0
Event Counter Byte 0. Increments on programmed edge event on CNT input. Nonvolatile when NVC=1,
Battery-backed when NVC=0, read/write.
0Dh
NVC
Event Counter Control
D7
D6
D5
D4
D3
D2
D1
D0
NVC
-
-
-
RC
WC
POLL
CP
Nonvolatile/Volatile Counter: Setting this bit to 1 makes the counter nonvolatile and counter operates only when
VDD is greater than VTP. Setting this bit to 0 makes the counter volatile, which allows counter operation under
VBAK or VDD power. If the NVC bit is changed, the counter value is not valid. Nonvolatile, read/write.
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 15 of 28
FM33256B SPI Companion w/ FRAM
RC
CP
Read Counter. Setting this bit to 1 takes a snapshot of the two counter bytes allowing the system to read the
values without missing count events. The RC bit will be automatically cleared.
Write Counter. Setting this bit to a 1 allows the user to write the counter bytes. While WC=1, the counter is
blocked from count events on the CNT pin. The WC bit must be cleared by the user to activate the counter.
Polled Mode: When POLL=1, the CNT pin is sampled for 30µs every 125ms. If POLL is set, the NVC bit is
internally cleared and the CP bit is set to detect a rising edge. The RTC oscillator must be enabled (/OSCEN=0)
to operate in polled mode. When POLL=0, CNT pin is continuously active. Nonvolatile, read/write.
The CNT pin detects falling edges when CP = 0, rising edges when CP = 1. Nonvolatile, read/write.
0Ch
Watchdog Control
WC
POLL
D7
D6
D5
D4
D3
D2
D1
D0
WDE
-
-
WDET4
WDET3
WDET2
WDET1
WDET0
WDE
Watchdog Enable: When WDE=1, a watchdog timer fault will cause the /RST signal to go active. When WDE =
0 the timer runs but has no effect on the /RST pin. Nonvolatile, read/write.
WDET(4:0) Watchdog EndTime: Sets the ending time for the watchdog window timer with 60 ms (min.) resolution. The
window timer allow independent leading and trailing edges (start and end of window) to be set. New watchdog
timeouts are loaded when the timer is restarted by writing the 1010b pattern to WR(3:0). To save power (disable
timer circuit), the EndTime may be set to all zeroes. Nonvolatile, read/write.
0Bh
Watchdog EndTime
Disables Timer
(min.)
(max.)
60 ms
200 ms
120 ms
400 ms
180 ms
600 ms
.
.
.
.
.
.
1200 ms
4000 ms
1260 ms
4200 ms
1320 ms
4400 ms
.
.
.
.
.
.
1740 ms
5800 ms
1800 ms
6000 ms
1860 ms
6200 ms
Watchdog Control
WDET4 WDET3 WDET2 WDET1 WDET0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
0
1
1
1
1
0
0
0
1
1
1
0
0
1
0
1
0
1
1
1
1
1
1
1
1
1
0
1
1
1
0
1
D7
D6
D5
D4
D3
D2
D1
D0
-
-
-
WDST4
WDST3
WDST2
WDST1
WDST0
WDST(4:0) Watchdog StartTime. Sets the starting time for the watchdog window timer with 25 ms (max.) resolution. The
window timer allow independent leading and trailing edges (start and end of window) to be set. New watchdog
timer settings are loaded when the timer is restarted by writing the 1010b pattern to WR(3:0). Nonvolatile,
read/write.
Watchdog StartTime
0 ms (default)
(min.)
(max.)
7.5 ms
25 ms
15.0 ms
50 ms
22.5 ms
75 ms
.
.
.
.
.
.
150 ms
500 ms
157.5 ms
525 ms
165 ms
550 ms
.
.
.
.
.
.
217.5 ms
725 ms
WDST4 WDST3 WDST2 WDST1 WDST0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
0
1
1
1
1
0
0
0
1
1
1
0
0
1
0
1
0
1
1
1
0
1
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 16 of 28
FM33256B SPI Companion w/ FRAM
0Ah
225 ms
232.5 ms
Watchdog Restart
750 ms
775 ms
1
1
1
1
1
1
1
1
0
1
D7
D6
D5
D4
D3
D2
D1
D0
-
-
-
-
WR3
WR2
WR1
WR0
WR(3:0)
Watchdog Restart. Writing a pattern 1010b to WR(3:0) restarts the watchdog timer. The upper nibble contents
do not affect this operation. Writing any pattern other than 1010b to WR3-0 has no effect on the watchdog.
Write-only.
09h
Watchdog Flags
EWDF
LWDF
POR
LB
08h
D7
D6
D5
D4
D3
D2
D1
D0
EWDF
LWDF
POR
LB
-
-
-
-
Early Watchdog Timer Fault Flag: When a watchdog restart occurs too early (before the programmed watchdog
StartTime), the /RST pin is driven low and this flag is set. It must be cleared by the user. Note that both EWDF
and POR could be set if both reset sources have occurred since the flags were cleared by the user. Batterybacked, read/write.
Late Watchdog Timer Fault Flag: When either a watchdog restart occurs too late (after the programmed
watchdog EndTime) or no restart occurs, the /RST pin is driven low and this flag is set. It must be cleared by the
user. Note that both LWDF and POR could be set if both reset sources have occurred since the flags were
cleared by the user. Battery-backed, read/write.
Power-On Reset: When the /RST signal is activated by VDD < VTP, the POR bit will be set to 1. A manual reset
will not set this flag. Note that one or both of the watchdog flags and the POR flag could be set if both reset
sources have occurred since the flags were cleared by the user. Battery-backed, read/write. (internally set, user
must clear bit)
Low Backup: If the VBAK source drops to a voltage level insufficient to operate the RTC/alarm when
VDD<VBAK, this bit will be set to ‘1’. All registers need to be re-initialized since the battery-backed register
values should be treated as unknown. The user should clear it to 0 when initializing the system. Battery-backed.
Read/Write (internally set, user must clear bit).
Timekeeping – Years
D7
D6
D5
D4
D3
D2
D1
D0
10 year.3
10 year.2
10 year.1
10 year.0
Year.3
Year.2
Year.1
Year.0
Contains the lower two BCD digits of the year. Lower nibble contains the value for years; upper nibble contains
the value for 10s of years. Each nibble operates from 0 to 9. The range for the register is 0-99. Battery-backed,
read/write.
07h
Timekeeping – Months
D7
D6
D5
D4
D3
D2
D1
D0
0
0
0
10 Month
Month.3
Month.2
Month.1
Month.0
Contains the BCD digits for the month. Lower nibble contains the lower digit and operates from 0 to 9; upper
nibble (one bit) contains the upper digit and operates from 0 to 1. The range for the register is 1-12. Batterybacked, read/write.
06h
Timekeeping – Date of the month
D7
D6
D5
D4
D3
D2
D1
D0
0
0
10 date.1
10 date.0
Date.3
Date.2
Date.1
Date.0
Contains the BCD digits for the date of the month. Lower nibble contains the lower digit and operates from 0 to
9; upper nibble contains the upper digit and operates from 0 to 3. The range for the register is 1-31. Batterybacked, read/write.
05h
Timekeeping – Day of the week
D7
D6
D5
D4
D3
D2
D1
D0
0
0
0
0
0
Day.2
Day.1
Day.0
Lower nibble contains a value that correlates to day of the week. Day of the week is a ring counter that counts
from 1 to 7 then returns to 1. The user must assign meaning to the day value, as the day is not integrated with the
date. Battery-backed, read/write.
04h
Timekeeping – Hours
D7
D6
D5
D4
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
D3
D2
D1
D0
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 17 of 28
FM33256B SPI Companion w/ FRAM
0
0
10 hours.1
10 hours.0
Hours.3
Hours2
Hours.1
Hours.0
Contains the BCD value of hours in 24-hour format. Lower nibble contains the lower digit and operates from 0
to 9; upper nibble (two bits) contains the upper digit and operates from 0 to 2. The range for the register is 0-23.
Battery-backed, read/write.
03h
Timekeeping – Minutes
D7
D6
D5
D4
D3
D2
D1
D0
0
10 min.2
10 min.1
10 min.0
Min.3
Min.2
Min.1
Min.0
Contains the BCD value of minutes. Lower nibble contains the lower digit and operates from 0 to 9; upper nibble
contains the upper minutes digit and operates from 0 to 5. The range for the register is 0-59. Battery-backed,
read/write.
02h
Timekeeping – Seconds
D7
D6
D5
D4
D3
D2
D1
D0
0
10 sec.2
10 sec.1
10 sec.0
Seconds.3
Seconds.2
Seconds.1
Seconds.0
Contains the BCD value of seconds. Lower nibble contains the lower digit and operates from 0 to 9; upper nibble
contains the upper digit and operates from 0 to 5. The range for the register is 0-59. Battery-backed, read/write.
01h
CALS
CAL.4-0
00h
/OSCEN
AF
CF
AEN
CAL
W
R
Reserved
CAL/Control
D7
D6
D5
D4
D3
D2
D1
D0
-
-
CALS
CAL.4
CAL.3
CAL.2
CAL.1
CAL.0
Calibration Sign: Determines if the calibration adjustment is applied as an addition to or as a subtraction from the
time-base. This bit can be written only when CAL=1. Nonvolatile, read/write.
Calibration Code: These five bits control the calibration of the clock. These bits can be written only when
CAL=1. Nonvolatile, read/write.
RTC/Alarm Control
D7
D6
D5
D4
D3
D2
D1
D0
OSCEN
AF
CF
AEN
Reserved
CAL
W
R
Oscillator Enable. When set to ‘1’, the oscillator is halted. When set to ‘0’, the oscillator runs. Disabling the
oscillator can save battery power during storage. On a power-up without a VBAK source or on a power-up after a
VBAK source has been applied, this bit is internally set to ‘1’, which turns off the oscillator. Battery-backed,
read/write.
Alarm Flag: This bit is set to 1 when the time and date match the values stored in the alarm registers with the
Match bit(s) = 0. The user must clear it to ‘0’. Battery-backed. (internally set, user must clear bit)
Century Overflow Flag: This bit is set to a 1 when the values in the years register overflows from 99 to 00. This
indicates a new century, such as going from 1999 to 2000 or 2099 to 2100. The user should record the new
century information as needed. The user must clear the CF bit to ‘0’. Battery-backed. (internally set, user must
clear bit)
Alarm Enable: This bit enables the alarm function. When AEN is set (and CAL cleared), the ACS pin operates as
an active-low alarm. The state of the ACS pin is detailed in Table 2. When AEN is cleared, no new alarm events
that set the AF bit will be generated. Clearing the AEN bit does not automatically clear AF. Battery-backed.
Calibration Mode: When CAL is set to 1, the clock enters calibration mode. When CAL is set to 0, the clock
operates normally, and the ACS pin is controlled by the RTC alarm. Battery-backed, read/write.
Write Time. Setting the W bit to 1 freezes updates of the user timekeeping registers. The user can then write
them with updated values. Setting the W bit to 0 causes the contents of the time registers to be transferred to the
timekeeping counters. Battery-backed, read/write.
Read Time. Setting the R bit to ‘1’ copies a static image of the timekeeping core and places it into the user
registers. The user can then read them without concerns over changing values causing system errors. The R bit
going from 0 to 1 causes the timekeeping capture, so the bit must be returned to 0 prior to reading again. Batterybacked, read/write.
Reserved bits. Do not use. Should remain set to 0.
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 18 of 28
FM33256B SPI Companion w/ FRAM
Serial Peripheral Interface – SPI Bus
The FM33256B employs a Serial Peripheral
Interface (SPI) bus. It is specified to operate at
speeds
up
to
16 MHz. This high-speed serial bus provides high
performance serial communication to a host
microcontroller. Many common microcontrollers
have hardware SPI ports allowing a direct interface.
It is quite simple to emulate the port using ordinary
port pins for microcontrollers that do not. The
FM33256B device operate in SPI Mode 0 and 3.
the bus master, the FM33256B will begin monitoring
the clock and data lines. The relationship between
the falling edge of /CS, the clock and data is dictated
by the SPI mode. The device will make a
determination of the SPI mode on the falling edge of
each chip select. While there are four such modes,
SCK
MOSI
MISO
SO
SPI
Microcontroller
SI SCK
SO
SI SCK
FM33256B
FM25W256
CS
CS
the FM33256B supports only modes 0 and 3. Figure
15 shows the required signal relationships for modes
0 and 3. For both modes, data is clocked into the
FM33256B on the rising edge of SCK and data is
expected on the first rising edge after /CS goes
active. If the clock starts from a high state, it will fall
prior to the first data transfer in order to create the
first rising edge.
The SPI interface uses a total of four pins: clock,
data-in, data-out, and chip select. A typical system
configuration uses an FM33256B and a standalone
SPI device with a microcontroller that has a
dedicated SPI port, as Figure 13 illustrates. Note that
the clock, data-in, and data-out pins are common
among all devices. The /CS pins must be driven
separately for the FM33256B and each additional
SPI device.
Protocol Overview
The SPI interface is a synchronous serial interface
using clock and data pins. It is intended to support
multiple devices on the bus. Each device is activated
using a chip select. Once chip select is activated by
SPI Mode 0: CPOL=0, CPHA=0
SS1
SS2
MOSI: Master Out, Slave In
MISO: Master In, Slave Out
SS: Slave Select
Figure 13. System Configuration with SPI port
For a microcontroller that has no dedicated SPI bus,
a general purpose port may be used. To reduce
hardware resources on the controller, it is possible to
connect the two data pins together. Figure 14 shows
a configuration that uses only three pins.
6
7
SO
SI
0
SPI Mode 3: CPOL=1, CPHA=1
7
Microcontroller
1
6
1
0
SCK
FM33256B
Figure 15. SPI Modes 0 & 3
CS
Figure 14. System Configuration without SPI port
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
The SPI protocol is controlled by op-codes. These
op-codes specify the commands to the device. After
/CS is activated the first byte transferred from the
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 19 of 28
FM33256B SPI Companion w/ FRAM
bus master is the op-code. Following the op-code,
any addresses and data are then transferred. Note that
the WREN and WRDI op-codes are commands with
no subsequent data transfer.
RDSR
WRSR
READ
WRITE
RDPC
WRPC
Important: The /CS pin must go inactive after an
operation is complete and before a new op-code
can be issued. There is only one valid op-code per
active chip select.
0101b
0001b
0011b
0010b
0011b
0010b
Sending the WREN op-code causes the internal
Write Enable Latch to be set. A flag bit in the Status
Register, called WEL, indicates the state of the latch.
WEL=1 indicates that writes are permitted.
Attempting to write the WEL bit in the Status
Register has no effect on the state of this bit. The
WEL bit will automatically be cleared on the rising
edge of /CS following a WRDI, WRSR, WRPC, or
WRITE op-code. No other op-code affects the state
of the WEL bit. This prevents further writes to the
Status Register, F-RAM memory, or the companion
register space without another WREN command.
Figure 16 below illustrates the WREN command bus
configuration.
Command Structure
There are eight commands called op-codes that can
be issued by the bus master to the FM33256B. They
are listed in the table below. These op-codes control
the functions performed by the memory and
Processor Companion. They can be divided into
three categories. First, there are commands that have
no subsequent operations. They perform a single
function, such as, enabling a write operation. Second
are commands followed by one data byte, either in or
out. They operate on the Status Register. The third
group includes commands for memory and Processor
Companion transactions followed by address and
one or more bytes of data.
WRDI – Write Disable
The WRDI command disables all write activity by
clearing the Write Enable Latch. The user can verify
that writes are disabled by reading the WEL bit in
the Status Register and verifying that WEL=0.
Figure 17 illustrates the WRDI command bus
configuration.
Table 5. Op-code Commands
Description
Op-code
Set Write Enable Latch
Write Disable
0000
0000
0000
0000
0001
0001
WREN – Set Write Enable Latch
The FM33256B will power up with writes disabled.
The WREN command must be issued prior to any
write operation. Sending the WREN op-code will
allow the user to issue subsequent op-codes for write
operations. These include writing the Status
Register, writing the Processor Companion, and
writing the memory.
Data Transfer
All data transfers to and from the FM33256B occur
in 8-bit groups. They are synchronized to the clock
signal (SCK), and they transfer most significant bit
(MSB) first. Serial inputs are registered on the rising
edge of SCK. Outputs are driven from the falling
edge of SCK.
Name
WREN
WRDI
Read Status Register
Write Status Register
Read Memory Data
Write Memory Data
Read Proc. Companion
Write Proc. Companion
0000 0110b
0000 0100b
CS
0
1
2
3
4
5
6
7
0
1
1
0
SCK
SI
SO
0
0
0
0
Hi-Z
Figure 16. WREN Bus Configuration
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 20 of 28
FM33256B SPI Companion w/ FRAM
CS
0
1
2
3
4
5
6
7
0
1
0
0
SCK
SI
0
0
0
0
Hi-Z
SO
Figure 17. WRDI Bus Configuration
RDSR – Read Status Register
The RDSR command allows the bus master to verify
the contents of the Status Register. Reading this
register provides information about the current state
of the write protection bits. Following the RDSR opcode, the FM33256B will return one byte with the
contents of the Status Register. The Status Register
is described in detail in a later section.
WRSR – Write Status Register
The WRSR command allows the user to select
certain write protection features by writing a byte to
the Status Register. Prior to sending the WRSR
command, the user must send a WREN command to
enable writes. Note that executing a WRSR
command is a write operation and therefore clears
the Write Enable Latch. The bus timings of RDSR
and WRSR are shown below.
Figure 18. RDSR Bus Configuration
Figure 19. WRSR Bus Configuration
(WREN must precede WRSR)
RDPC – Read Processor Companion
The RDPC command allows the bus master to verify
the contents of the Processor Companion registers.
Following the RDPC op-code, a single-byte register
address is sent. The FM33256B will then return one
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
or more bytes with the contents of the companion
registers. When reading multiple data bytes, the
nternal register address will wrap around to 00h after
1Dh is reached.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 21 of 28
FM33256B SPI Companion w/ FRAM
program the companion registers. When writing
multiple data bytes, the internal register address will
wrap around to 00h after 1Dh is reached. The rising
edge of /CS terminates a WRPC operation. See
Figure 21.
WRPC – Write Processor Companion
The WRPC command is used to set companion
control settings. A WREN command is required
prior to sending the WRPC command. Following the
WRPC op-code, a single-byte register address is
sent. The controller then drives one or more bytes to
CS
0
1
2
0
0
0
3
4
5
6
7
0
1
0
1
1
7
6
2
3
4
5
6
Register Address
5 4 3 2
1
7
0
1
2
3
4
5
6
7
7
7 6
MSB
5
Data Out
4 3 2
1
0
LSB
0
LSB
SCK
op-code
SI
1
0
MSB
0
LSB
Hi-Z
SO
Figure 20. Processor Companion Read
CS
0
1
2
3
4
5
6
7
0
1
0
1
0
7
6
2
3
4
5
6
7
0
1
2
3
4
5
6
Register Address
5 4 3 2 1
0
7
6
5
Data
4 3
2
1
7
7
SCK
op-code
SI
0
0
0
1
0
MSB
LSB MSB
0
0
LSB
LSB
Hi-Z
SO
Figure 21. Processor Companion Write
(WREN must precede WRPC)
Status Register & Write Protection
The write protection features of the FM33256B are
multi-tiered. To write the memory, a WREN op-code
must first be issued, followed by a WRITE op-code.
A Status Register associated with the memory has a
write enable latch bit (WEL) that is internally set
when WREN is issued.
Writes to certain memory blocks are controlled by
the Block Protect bits in the Status Register. The BP
bits may be changed by using the WRSR command.
The Status Register is organized as follows.
and BP0 control software write-protection features.
They are nonvolatile (shaded yellow). The WEL flag
indicates the state of the Write Enable Latch.
Attempting to directly write the WEL bit in the Status
Register has no effect on its state, since this bit is
internally set and cleared via the WREN and WRDI
commands, respectively. BP1 and BP0 are memory
block write protection bits. They specify portions of
memory that are write-protected as shown in the
following table.
Table 6. Status Register
Bit
Name
7
0
6
1
5
0
4
0
3
BP1
2
BP0
1
WEL
0
0
Bits 7, 5, 4, and 0 are fixed at 0, bit 6 is fixed at 1,
and none of these bits can be modified. Note that bit
0 (Ready in EEPROMs) is unnecessary as the FRAM writes in real-time and is never busy. The BP1
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Table 7. Block Memory Write Protection
BP1
BP0
Protected Address Range
0
0
None
0
1
Upper ¼
1
0
Upper ½
1
1
All
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 22 of 28
FM33256B SPI Companion w/ FRAM
The BP1 and BP0 bits and the Write Enable Latch
are the only mechanisms that protect the memory
from writes.
operation. A write operation is shown in Figure 22.
Note: Although the WREN op-code is not shown in
the timing diagram, it is required prior to sending the
WRITE command.
Memory Operation
The SPI interface, which is capable of a relatively
high clock frequency, highlights the fast write
capability of the F-RAM technology. Unlike SPI-bus
EEPROMs, the FM33256B can perform sequential
writes at bus speed. No page register is needed and
any number of sequential writes may be performed.
EEPROMs use page buffers to increase their write
throughput. This compensates for the technology’s
inherently slow write operations. F-RAM memories
do not have page buffers because each byte is written
to the F-RAM array immediately after it is clocked in
(after the 8th clock). This allows any number of bytes
to be written without page buffer delays.
Write Operation
All writes to the memory begin with a WREN opcode with /CS being asserted and deasserted. The
next op-code is a WRITE. The WRITE op-code is
followed by a two-byte address value. This is the
starting address of the first data byte of the write
operation. Subsequent bytes are data bytes, which are
written sequentially. Addresses are incremented
internally as long as the bus master continues to issue
clocks and keeps /CS low. A write operation will be
terminated when a write-protected address is directly
accessed or when the device has internally
incremented the address into a write-protected space.
If the last address (7FFFh) is reached, the counter
will roll over to 0000h. Data is written MSB first.
The rising edge of /CS terminates a WRITE
Read Operation
After the falling edge of /CS, the bus master can issue
a READ op-code. Following the READ command is
a two-byte address value. This is the starting address
of the first byte of the read operation. After the opcode and address are issued, the device drives out the
read data on the next 8 clocks. The SI input is
ignored during read data bytes. Subsequent bytes are
data bytes, which are read out sequentially.
Addresses are incremented internally as long as the
bus master continues to issue clocks and /CS is low.
If the last address is reached (7FFFh), the counter
will roll over to 0000h. Data is read MSB first. The
rising edge of /CS terminates a READ operation. A
read operation is shown in Figure 23.
CS
0
1
2
3
4
5
6
7
0
1
2
14
13
3
4
6
7
0
1
2
6
5
3
4
5
6
3
2
1
7
7
SCK
SI
0
0
0
Op-code
0
0
X
12
11
1
MSB
Hi-Z
SO
Data In
16-bit Address
1
0
0
0
LSB
7
4
MSB
0
0
LSB
Figure 22. Memory Write
(WREN must precede WRITE)
CS
0
1
2
3
4
5
6
0
7
1
2
14
13
3
4
6
7
0
1
2
3
4
5
6
6
5
Data Out
4
3
2
1
7
7
SCK
SI
0
SO
0
0
Op-code
0
Hi-Z
16-bit Address
0
0
1
1
X
12
11
MSB
1
0
LSB
7
MSB
0
0
LSB
Figure 23. Memory Read
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 23 of 28
FM33256B SPI Companion w/ FRAM
Electrical Specifications
Absolute Maximum Ratings
Symbol
Description
VDD
Power Supply Voltage with respect to VSS
VIN
Voltage on any signal pin with respect to VSS
VBAK
TSTG
TLEAD
VESD
Ratings
-1.0V to +5.0V
-1.0V to +5.0V and
VIN < VDD+1.0V
-1.0V to +4.5V
-55°C to + 125°C
260° C
Backup Supply Voltage
Storage Temperature
Lead Temperature (Soldering, 10 seconds)
Electrostatic Discharge Voltage
- Human Body Model (JEDEC Std JESD22-A114-E)
- Charged Device Model (JEDEC Std JESD22-C101-C)
- Machine Model (JEDEC Std JESD22-A115-A)
Package Moisture Sensitivity Level
TBD
TBD
TBD
MSL-1
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating
only, and the functional operation of the device at these or any other conditions above those listed in the operational section of this
specification is not implied. Exposure to absolute maximum ratings conditions for extended periods may affect device reliability.
DC Operating Conditions (TA = -40° C to + 85° C, VDD = 2.7V to 3.6V unless otherwise specified)
Symbol
Parameter
Min
Typ
Max
VDD
Main Power Supply
2.7
3.6
IDD
VDD Supply Current (VBC=0)
@ SCK = 1.0 MHz
1.1
@ SCK = 16.0 MHz
16.0
ISB
Standby Current
Trickle Charger Off (VBC=0)
150
VBAK
RTC Backup Voltage
@ TA = +25ºC to +85ºC
1.55
3.75
@ TA = -40ºC to +25ºC
1.90
3.75
IBAK
RTC Backup Current
@ TA = +25ºC, VBAK = 3.0V
1.4
@ TA = +85ºC, VBAK = 3.0V
2.0
@ TA = +25ºC, VBAK = 2.0V
1.15
@ TA = +85ºC, VBAK = 2.0V
1.65
IBAKTC
IQTC
IQWD
VTP0
VTP1
VTP2
VTP3
VRST
VSW
ILI
ILO
VIL
Trickle Charge Current with VBAK=0V
Fast Charge Off (FC = 0)
Fast Charge On (FC = 1)
VDD Quiescent Current (VBC=1)
VDD Quiescent Current (WDE=1)
VDD Trip Point Voltage, VTP(1:0) = 00b
VDD Trip Point Voltage, VTP(1:0) = 01b
VDD Trip Point Voltage, VTP(1:0) = 10b
VDD Trip Point Voltage, VTP(1:0) = 11b
VDD for valid /RST @ IOL = 80 µA at VOL
VBAK > VBAK min
VBAK < VBAK min
Battery Switchover Voltage
Input Leakage Current
Output Leakage Current
Input Low Voltage
All inputs except as listed below
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
50
200
2.53
2.68
2.78
2.91
0
1.6
2.0
-0.3
2.6
2.75
2.9
3.0
Units
V
Notes
1
2
mA
mA
µA
V
µA
µA
µA
µA
3
4
5
6
200
2500
70
30
2.72
2.87
2.99
3.15
µA
µA
µA
µA
V
V
V
V
2.7
±1
±1
V
V
V
µA
µA
11
11
0.3 VDD
V
12
7
8
9
9
9
9
10
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 24 of 28
FM33256B SPI Companion w/ FRAM
CNT battery-backed (VDD < VSW)
CNT (VDD > VSW)
-0.3
-0.3
0.5
0.8
V
V
DC Operating Conditions, continued (TA = -40° C to + 85° C, VDD = 2.7V to 3.6V unless otherwise specified)
Symbol Parameter
Min
Typ
Max
Units
VIH
Input High Voltage
All inputs except as listed below
0.7 VDD
VDD + 0.3
V
VBAK – 0.5
CNT battery-backed (VDD < VSW)
VBAK + 0.3
V
CNT VDD > VSW
0.7 VDD
VDD + 0.3
V
PFI
VDD + 0.3
V
VOL
Output Low Voltage @ IOL = 3 mA
0.4
V
VOH
Output High Voltage
(SO, PFO) @ IOH = -2 mA
VDD – 0.8
V
RRST
Pull-up resistance for /RST inactive
50
400
KΩ
VPFI
Power Fail Input Reference Voltage
1.475
1.50
1.525
V
VHYS
Power Fail Input (PFI) Hysteresis (Rising)
100
mV
Notes
Notes
1. Full complete operation. Supervisory circuits, RTC, etc operate to lower voltages as specified.
2. SCK toggling between VDD-0.3V and VSS, other inputs VSS or VDD-0.3V.
3. All inputs at VSS or VDD, static. Trickle charger off (VBC=0).
4. The VBAK trickle charger automatically regulates the maximum voltage on this pin for capacitor backup applications.
5. VDD < VSW, oscillator running, CNT at VBAK.
6. VBAK will source current when trickle charge is enabled (VBC bit=1), VDD > VBAK, and VBAK < VBAK max.
7. This is the VDD supply current contributed by enabling the trickle charger circuit, and does not account for IBAKTC.
8. This is the VDD supply current contributed by enabling the watchdog circuit, WDE=1 and WDET set to a non-zero value.
9. /RST is asserted active when VDD < VTP .
10. The minimum VDD to guarantee the level of /RST remains a valid VOL level.
11. VIN or VOUT = VSS to VDD. Does not apply to PFI, X1, or X2.
12. Includes /RST input detection of external reset condition to trigger driving of /RST signal by FM33256B.
AC Parameters (TA = -40°C to + 85°C, VDD = 2.7V to 3.6V CL = 30 pF)
Symbol
Parameter
Min
fCK
SCK Clock Frequency
0
tCH
Clock High Time
28
tCL
Clock Low Time
28
tCSU
Chip Select Setup
10
tCSH
Chip Select Hold
10
tOD
Output Disable Time
tODV
Output Data Valid Time
tOH
Output Hold Time
0
tD
Deselect Time
90
tR
Data In Rise Time
tF
Data In Fall Time
tSU
Data Setup Time
6
tH
Data Hold Time
6
Max
16
20
24
50
50
Units
MHz
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
Notes
1
1
2
1,3
1,3
Notes
1. tCH + tCL = 1/fCK.
2. This parameter is characterized but not 100% tested.
3. Rise and fall times measured between 10% and 90% of waveform.
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 25 of 28
FM33256B SPI Companion w/ FRAM
Capacitance (TA = 25° C, f=1.0 MHz, VDD = 3.0V)
Symbol
Parameter
CIO
Input/Output Capacitance
CXTL
X1, X2 Crystal pin Capacitance
CCNT
Max. Allowable Capacitance on CNT (polled mode)
Typ
25
-
Max
8
100
Units
pF
pF
pF
Notes
1
1, 2
Notes
1
This parameter is characterized but not tested.
2
The crystal attached to the X1/X2 pins must be rated as 12.5pF.
Supervisor Timing (TA = -40° C to + 85° C, VDD = 2.7V to 3.6V)
Symbol
Parameter
tRPU
/RST Active (low) after VDD>VTP
tRNR
/RST Response Time to VDD<VTP (noise filter)
tVR
VDD Rise Time
tVF
VDD Fall Time
tWDST
Watchdog StartTime
tWDET
Watchdog EndTime
fCNT
Frequency of Event Counter
Min
30
7
50
100
0.3*tDOG1
tDOG2
0
Max
100
25
100,000
tDOG1
3.3*tDOG2
1
Units
ms
µs
µs/V
µs/V
ms
ms
kHz
Notes
4
1
1,2
1,2
3
3
Notes
1
This parameter is characterized but not tested.
2
Slope measured at any point on VDD waveform.
3
tDOG1 is the programmed StartTime and tDOG2 is the programmed EndTime in registers 0Bh and 0Ch, VDD > VTP, and tRPU
satisfied. The StartTime has a resolution of 25ms. The EndTime has a resolution of 60ms.
4
The /RST pin will drive low for this length of time after the internal reset circuit is activated due to a watchdog, low voltage,
or manual reset event.
Data Retention (VDD = 2.7V to 3.6V)
Symbol
Parameter
TDR
Data Retention
@ +75°C
@ +80°C
@ +85°C
AC Test Conditions
Input Pulse Levels
Input Rise and Fall Times
Input and Output Timing Levels
Output (SO) Load Capacitance
Min
Units
38
19
10
Years
Years
Years
Notes
10% and 90% of VDD
5 ns
0.5 VDD
30 pF
Diagram Notes
All timing parameters apply to both read and write cycles. Clock specifications are identical for read and write cycles. Write
timing parameters apply to op-code, word address, and write data bits. Functional relationships are illustrated in the relevant data
sheet sections. These diagrams illustrate the timing parameters only.
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 26 of 28
FM33256B SPI Companion w/ FRAM
Serial Data Bus Timing
tD
CS
tCSU
tF
1/fCK
tCL
tR
tCH
tCSH
SCK
tSU
tH
SI
tODV
/RST Timing
tOH
tOD
SO
VDD
VTP
t VF
t VR
VRST
tRNR
tRPU
RST
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 27 of 28
FM33256B SPI Companion w/ FRAM
Mechanical Drawing
14-pin SOIC (JEDEC Standard MS-012 variation AB)
Recommended PCB Footprint
...
7.70
3.70
6.00 ±0.20
3.90 ±0.13
...
2.00
0.65
1.27
Pin 1
8.64 ±0.10
1.27
0.33
0.51
0.25
0.50
1.35
1.75
0.10
0.25
0.10 mm
0.19
0.25
45 
0- 8
0.40
1.27
All dimensions in millimeters.
Conversions to inches are not exact.
SOIC Package Marking Scheme
XXXXXXX-P
LLLLLLL
RIC YYWW
Legend:
XXXX= part number, P= package type (-G)
LLLLLLL= lot code
RIC=Ramtron Int’l Corp, YY=year, WW=work week
Example: FM33256B, “Green” SOIC package, Year 2011, Work Week 40
FM33256B-G
AL3902G
RIC 1140
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 28 of 28
FM33256B SPI Companion w/ FRAM
Revision History
Revision
0.1
0.2
1.0
1.1
3.0
Date
6/28/2011
10/7/2011
1/6/2012
2/10/2012
7/18/2012
Summary
Initial release.
Minor edits.
Changed to Preliminary status.
Added timing parameter for oscillator startup.
Added Vtp data and changed to production status
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
Rev. 3.0
Aug. 2012
Page 29 of 28