ETC 24LC21AT-I/SN

24LC21A
1K 2.5V Dual Mode I2C™ Serial EEPROM
FEATURES
PDIP
NC
1
NC
2
NC
3
VSS
4
24LC21A
8
VCC
7
VCLK
6
SCL
5
SDA
SOIC
NC
1
NC
2
NC
3
VSS
4
24LC21A
• Single supply with operation down to 2.5V
• Completely implements DDC1/DDC2
interface for monitor identification, including
recovery to DDC1
• Pin and function compatible with 24LC21
• Low power CMOS technology
- 1 mA typical active current
- 10 µA standby current typical at 5.5V
• 2-wire serial interface bus, I2C compatible
• 100 kHz (2.5V) and 400 kHz (5V) compatibility
• Self-timed write cycle (including auto-erase)
• Page-write buffer for up to eight bytes
• 1,000,000 erase/write cycles guaranteed
• Data retention > 200 years
• ESD Protection > 4000V
• 8-pin PDIP and SOIC package
• Available for extended temperature ranges
- Commercial (C):
0°C to +70°C
- Industrial (I):
-40°C to +85°C
PACKAGE TYPES
8
VCC
7
VCLK
6
SCL
5
SDA
DESCRIPTION
The Microchip Technology Inc. 24LC21A is a 128 x 8bit dual-mode Electrically Erasable PROM. This device
is designed for use in applications requiring storage
and serial transmission of configuration and control
information. Two modes of operation have been implemented: Transmit-Only Mode and Bi-directional Mode.
Upon power-up, the device will be in the Transmit-Only
Mode, sending a serial bit stream of the memory array
from 00h to 7Fh, clocked by the VCLK pin. A valid high
to low transition on the SCL pin will cause the device to
enter the transition mode, and look for a valid control
byte on the I2C bus. If it detects a valid control byte from
the master, it will switch into Bi-directional Mode, with
byte selectable read/write capability of the memory
array using SCL. If no control byte is received, the
device will revert to the Transmit-Only Mode after it
receives 128 consecutive VCLK pulses while the SCL
pin is idle. The 24LC21A is available in a standard 8-pin
PDIP and SOIC package in both commercial and
industrial temperature ranges.
BLOCK DIAGRAM
HV GENERATOR
I/O
CONTROL
LOGIC
MEMORY
CONTROL
LOGIC
XDEC
EEPROM
ARRAY
PAGE LATCHES
SDA
SCL
YDEC
VCLK
VCC
SENSE AMP
R/W CONTROL
VSS
DDC is a trademark of the Video Electronics Standards Association.
I2C is a trademark of Philips Corporation.
 1999 Microchip Technology Inc.
DS21160E-page 1
24LC21A
1.0
1.1
ELECTRICAL
CHARACTERISTICS
TABLE 1-1:
PIN FUNCTION TABLE
Name
Function
VSS
SDA
SCL
VCLK
VCC
NC
Ground
Serial Address/Data I/O
Serial Clock (Bi-directional Mode)
Serial Clock (Transmit-Only Mode)
+2.5V to 5.5V Power Supply
No Connection
Maximum Ratings*
VCC ........................................................................7.0V
All inputs and outputs w.r.t. VSS .....-0.6V to VCC +1.0V
Storage temperature ..........................-65°C to +150°C
Ambient temp. with power applied......-65°C to +125°C
Soldering temperature of leads (10 seconds) .. +300°C
ESD protection on all pins ..................................... ≥ 4 kV
*Notice: Stresses above those listed under “Maximum ratings” may cause permanent damage to the device. This is a stress rating only and functional operation of
the device at those or any other conditions above those indicated in the operational
listings of this specification is not implied. Exposure to maximum rating conditions
for extended periods may affect device reliability.
TABLE 1-2:
DC CHARACTERISTICS
VCC = +2.5V to 5.5V
Commercial (C): Tamb = 0°C to +70°C
Industrial (I):
Tamb =-40°C to +85°C
Parameter
Symbol
Min
Max
Units
SCL and SDA pins:
High level input voltage
Low level input voltage
VIH
VIL
0.7 VCC
—
—
0.3 VCC
V
V
Input levels on VCLK pin:
High level input voltage
Low level input voltage
VIH
VIL
2.0
—
—
0.2 VCC
V
V
VCC ≥ 2.7V (Note)
VCC < 2.7V (Note)
Hysteresis of Schmitt trigger inputs
VHYS
.05 VCC
—
V
(Note)
Low level output voltage
VOL1
—
0.4
V
IOL = 3 mA, VCC = 2.5V (Note)
Low level output voltage
VOL2
—
0.6
V
IOL = 6 mA, VCC = 2.5V
Input leakage current
ILI
-10
10
µA
VIN = 0.1V to VCC
Output leakage current
ILO
-10
10
µA
VOUT = 0.1V to VCC
Pin capacitance (all inputs/outputs)
Cin, Cout
—
10
pF
VCC = 5.0V (Note)
Tamb = 25°C, FCLK = 1 MHz
Operating current
ICC Write
ICC Read
—
—
3
1
mA
mA
VCC = 5.5V
VCC = 5.5V, SCL = 400 kHz
ICCS
—
—
30
100
µA
µA
VCC = 3.0V, SDA = SCL = VCC
VCC = 5.5V, SDA = SCL = VCC
VCLK = VSS
Standby current
Note:
Conditions
This parameter is periodically sampled and not 100% tested.
DS21160E-page 2
 1999 Microchip Technology Inc.
24LC21A
TABLE 1-3:
AC CHARACTERISTICS
Parameter
Symbol
Vcc= 2.5-5.5V
Standard Mode
Vcc= 4.5 - 5.5V
Fast Mode
Min
Max
Min
Max
Units
Remarks
Clock frequency
Clock high time
Clock low time
SDA and SCL rise time
SDA and SCL fall time
START condition hold time
FCLK
THIGH
TLOW
TR
TF
THD:STA
—
4000
4700
—
—
4000
100
—
—
1000
300
—
—
600
1300
—
—
600
400
—
—
300
300
—
kHz
ns
ns
ns
ns
ns
START condition setup
time
Data input hold time
Data input setup time
STOP condition setup time
Output valid from clock
Bus free time
TSU:STA
4700
—
600
—
ns
THD:DAT
TSU:DAT
TSU:STO
TAA
TBUF
0
250
4000
—
4700
—
—
—
3500
—
0
100
600
—
1300
—
—
—
900
—
ns
ns
ns
ns
ns
—
250
250
ns
—
50
20 + 0.1
CB
—
(Note 2)
Time the bus must be free
before a new transmission
can start
(Note 1), CB ≤ 100 pF
50
ns
(Note 3)
—
10
—
10
ms
Byte or Page mode
—
4000
4700
0
4000
—
0
2000
—
—
—
—
1000
—
—
600
1300
0
600
—
0
1000
—
—
—
—
500
—
ns
ns
ns
ns
ns
ns
ns
—
100
—
100
ns
1M
—
1M
—
cycles
TOF
Output fall time from VIH
minimum to VIL maximum
Input filter spike suppresTSP
sion (SDA and SCL pins)
Write cycle time
TWR
Transmit-Only Mode Parameters
Output valid from VCLK
TVAA
VCLK high time
TVHIGH
VCLK low time
TVLOW
VCLK setup time
TVHST
VCLK hold time
TSPVL
Mode transition time
TVHZ
Transmit-Only power up
TVPU
time
Input filter spike suppresTSPV
sion (VCLK pin)
Endurance
—
(Note 1)
(Note 1)
After this period the first clock
pulse is generated
Only relevant for repeated
START condition
(Note 2)
25°C, Vcc = 5.0V, Block
Mode (Note 4)
Note 1: Not 100% tested. CB = Total capacitance of one bus line in pF.
2: As a transmitter, the device must provide an internal minimum delay time to bridge the undefined region
(minimum 300 ns) of the falling edge of SCL to avoid unintended generation of START or STOP conditions.
3: The combined TSP and VHYS specifications are due to Schmitt trigger inputs which provide noise and spike
suppression. This eliminates the need for a TI specification for standard operation.
4: This parameter is not tested but guaranteed by characterization. For endurance estimates in a specific application, please consult the Total Endurance Model which can be obtained on our website.
 1999 Microchip Technology Inc.
DS21160E-page 3
24LC21A
2.0
FUNCTIONAL DESCRIPTION
Transmit-Only Mode (Section 2.2). In this mode, data
is transmitted on the SDA pin in 8-bit bytes, with each
byte followed by a ninth, null bit (Figure 2-1). The clock
source for the Transmit-Only Mode is provided on the
VCLK pin, and a data bit is output on the rising edge on
this pin. The eight bits in each byte are transmitted
most significant bit first. Each byte within the memory
array will be output in sequence. After address 7Fh in
the memory array is transmitted, the internal address
pointers will wrap around to the first memory location
(00h) and continue. The Bi-directional Mode Clock
(SCL) pin must be held high for the device to remain in
the Transmit-Only Mode.
The 24LC21A is designed to comply to the DDC Standard proposed by VESA (Figure 3-3) with the exception
that it is not Access.bus capable. It operates in two
modes, the Transmit-Only Mode and the Bi-directional
Mode. There is a separate 2-wire protocol to support
each mode, each having a separate clock input but
sharing a common data line (SDA). The device enters
the Transmit-Only Mode upon power-up. In this mode,
the device transmits data bits on the SDA pin in
response to a clock signal on the VCLK pin. The device
will remain in this mode until a valid high to low transition is placed on the SCL input. When a valid transition
on SCL is recognized, the device will switch into the Bidirectional Mode and look for its control byte to be sent
by the master. If it detects its control byte, it will stay in
the Bi-directional Mode. Otherwise, it will revert to the
Transmit-Only Mode after it sees 128 VCLK pulses.
2.1
2.2
After VCC has stabilized, the device will be in the
Transmit-Only Mode. Nine clock cycles on the VCLK
pin must be given to the device for it to perform internal
sychronization. During this period, the SDA pin will be
in a high impedance state. On the rising edge of the
tenth clock cycle, the device will output the first valid
data bit which will be the most significant bit in address
00h. (Figure 2-2).
Transmit-Only Mode
The device will power up in the Transmit-Only Mode at
address 00H. This mode supports a unidirectional
2-wire protocol for continuous transmission of the
contents of the memory array. This device requires that
it be initialized prior to valid data being sent in the
FIGURE 2-1:
Initialization Procedure
TRANSMIT-ONLY MODE
SCL
Tvaa
Tvaa
SDA
Null Bit
Bit 1 (LSB)
Bit 1 (MSB)
Bit 7
VCLK
Tvhigh Tvlow
FIGURE 2-2:
DEVICE INITIALIZATION
Vcc
SCL
SDA
Tvaa
High Impedance for 9 clock cycles
Tvaa
Bit 8
Bit 7
Tvpu
VCLK
DS21160E-page 4
1
2
8
9
10
11
 1999 Microchip Technology Inc.
24LC21A
3.0
BI-DIRECTIONAL MODE
Once the device has switched into the Bi-directional
Mode, the VCLK input is disregarded, with the exception that a logic high level is required to enable write
capability. This mode supports a two-wire Bi-directional
data transmission protocol (I2C). In this protocol, a
device that sends data on the bus is defined to be the
transmitter, and a device that receives data from the
bus is defined to be the receiver. The bus must be controlled by a master device that generates the Bi-directional Mode Clock (SCL), controls access to the bus
and generates the START and STOP conditions, while
the 24LC21A acts as the slave. Both master and slave
can operate as transmitter or receiver, but the master
device determines which mode is activated. In the Bidirectional mode, the 24LC21A only responds to
commands for device 1010 000X.
Before the 24LC21A can be switched into the Bi-directional Mode (Figure 3-1), it must enter the transition
mode, which is done by applying a valid high to low
transition on the Bi-directional Mode Clock (SCL). As
soon it enters the transition mode, it looks for a control
byte 1010 000X on the I2C bus, and starts to count
pulses on VCLK. Any high to low transition on the SCL
line will reset the count. If it sees a pulse count of 128
on VCLK while the SCL line is idle, it will revert back to
the Transmit-Only Mode, and transmit its contents
starting with the most significant bit in address 00h.
However, if it detects the control byte on the I2C bus,
(Figure 3-2) it will switch to the in the Bi-directional
Mode. Once the device has made the transition to the
Bi-directional mode, the only way to switch the device
back to the Transmit-Only Mode is to remove power
from the device. The mode transition process is shown
in detail in Figure 3-3.
FIGURE 3-1:
MODE
MODE TRANSITION WITH RECOVERY TO TRANSMIT-ONLY MODE
Transmit
Only
Recovery to Transmit-Only Mode
Bi-directional
TVHZ
SCL
(MSB of data in 00h)
Bit8
SDA
VCLK count =
1
2
3
4
127 128
VCLK
FIGURE 3-2:
SUCCESSFUL MODE TRANSITION TO BI-DIRECTIONAL MODE
Transmit
Only Mode
Transition Mode with possibility to return to Transmit-Only Mode
Bi-directional
permanently
MODE
SCL
SDA
VCLK count =
VCLK
1
2
n
S 1
0
0
1
0
0
0
0
0
ACK
n < 128
 1999 Microchip Technology Inc.
DS21160E-page 5
24LC21A
FIGURE 3-3:
DISPLAY OPERATION PER DDC STANDARD PROPOSED BY VESA
The 24LC21A was designed to
comply to the portion of flowchart inside dash box
Display Power-on
or
DDC Circuit Powered
from +5 volts
Communication
is idle
Is Vsync
present?
No
Yes
High to low
transition on
SCL?
Send EDID continuously
using Vsync as clock
No
Yes
High to low
transition on
SCL?
No
Yes
Stop sending EDID.
Switch to DDC2 mode.
Display has
optional
transition state
?
DDC2 communication
idle. Display waiting for
address byte.
No
DDC2B
address
received?
Yes
Set Vsync counter = 0
or start timer
Yes
Receive DDC2B
command
No
Reset counter or timer
Respond to DDC2B
command
Change on
SCL, SDA or
VCLK lines?
No
Yes
No
Is display
Access.busTM
capable?
High - low
transition on SCL
?
Yes
Yes
Reset Vsync counter = 0
Valid
DDC2 address
received?
No
Valid Access.bus
address?
No
Yes
Yes
No
No
VCLK
cycle?
See Access.bus
specification to determine
correct procedure.
Yes
Increment VCLK counter
(if appropriate)
No
Counter=128 or
timer expired?
Yes
Switch back to DDC1
mode.
Note 1: The base flowchart is copyright  1993, 1994, 1995 Video Electronic Standard Association (VESA) from
VESA’s Display Data Channel (DDC) Standard Proposal ver. 2p rev. 0, used by permission of VESA.
2: The dash box and text “The 24LC21A and... inside dash box.” are added by Microchip Technology, Inc.
3: Vsync signal is normally used to derive a signal for VCLK pin on the 24LC21A.
DS21160E-page 6
 1999 Microchip Technology Inc.
24LC21A
3.1
Bi-directional Mode Bus
Characteristics
The following bus protocol has been defined:
• Data transfer may be initiated only when the bus
is not busy.
• During data transfer, the data line must remain
stable whenever the clock line is HIGH. Changes
in the data line while the clock line is HIGH will be
interpreted as a START or STOP condition.
Each data transfer is initiated with a START condition
and terminated with a STOP condition. The number of
the data bytes transferred between the START and
STOP conditions is determined by the master device
and is theoretically unlimited, although only the last
eight will be stored when doing a write operation. When
an overwrite does occur it will replace data in a first in
first out fashion.
Note:
Accordingly, the following bus conditions have been
defined (Figure 3-4).
3.1.1
BUS NOT BUSY (A)
3.1.5
Both data and clock lines remain HIGH.
3.1.2
START DATA TRANSFER (B)
A HIGH to LOW transition of the SDA line while the
clock (SCL) is HIGH determines a START condition. All
commands must be preceded by a START condition.
3.1.3
3.1.4
DATA VALID (D)
The state of the data line represents valid data when,
after a START condition, the data line is stable for the
duration of the HIGH period of the clock signal.
The data on the line must be changed during the LOW
period of the clock signal. There is one clock pulse per
bit of data.
FIGURE 3-4:
(A)
ACKNOWLEDGE
Each receiving device, when addressed, is obliged to
generate an acknowledge after the reception of each
byte. The master device must generate an extra clock
pulse which is associated with this acknowledge bit.
Note:
STOP DATA TRANSFER (C)
A LOW to HIGH transition of the SDA line while the
clock (SCL) is HIGH determines a STOP condition. All
operations must be ended with a STOP condition.
Once switched into Bi-directional Mode, the
24LC21A will remain in that mode until
power is removed. Removing power is the
only way to reset the 24LC21A into the
Transmit-only mode.
The 24LC21A does not generate any
acknowledge
bits
if
an
internal
programming cycle is in progress.
The device that acknowledges has to pull down the
SDA line during the acknowledge clock pulse in such a
way that the SDA line is stable LOW during the HIGH
period of the acknowledge related clock pulse. Of
course, setup and hold times must be taken into
account. A master must signal an end of data to the
slave by not generating an acknowledge bit on the last
byte that has been clocked out of the slave. In this
case, the slave must leave the data line HIGH to enable
the master to generate the STOP condition.
DATA TRANSFER SEQUENCE ON THE SERIAL BUS
(B)
(D)
START
CONDITION
ADDRESS OR
ACKNOWLEDGE
VALID
(D)
(C)
(A)
SCL
SDA
 1999 Microchip Technology Inc.
DATA
ALLOWED
TO CHANGE
STOP
CONDITION
DS21160E-page 7
24LC21A
FIGURE 3-5:
BUS TIMING START/STOP
SCL
VHYS
THD:STA
TSU:STO
TSU:STA
SDA
START
FIGURE 3-6:
STOP
BUS TIMING DATA
TF
TR
THIGH
TLOW
SCL
TSU:STA
THD:DAT
TSU:DAT
THD:STA
SDA
IN
TSU:STO
TSP
TBUF
TAA
TAA
SDA
OUT
3.1.6
SLAVE ADDRESS
FIGURE 3-7:
After generating a START condition, the bus master
transmits the slave address consisting of a 7-bit device
code (1010000) for the 24LC21A.
Operation
Slave Address
R/W
Read
Write
1010000
1010000
1
0
DS21160E-page 8
READ/WRITE
START
The eighth bit of slave address determines whether the
master device wants to read or write to the 24LC21A
(Figure 3-7).
The 24LC21A monitors the bus for its corresponding
slave address continuously. It generates an
acknowledge bit if the slave address was true and it is
not in a programming mode.
CONTROL BYTE
ALLOCATION
R/W
SLAVE ADDRESS
1
0
1
0
0
0
A
0
 1999 Microchip Technology Inc.
24LC21A
4.0
WRITE OPERATION
4.2
4.1
Byte Write
The write control byte, word address and the first data
byte are transmitted to the 24LC21A in the same way
as in a byte write. But instead of generating a stop
condition the master transmits up to eight data bytes to
the 24LC21A which are temporarily stored in the onchip page buffer and will be written into the memory
after the master has transmitted a stop condition. After
the receipt of each word, the three lower order address
pointer bits are internally incremented by one. The
higher order five bits of the word address remains
constant. If the master should transmit more than eight
words prior to generating the stop condition, the
address counter will roll over and the previously
received data will be overwritten. As with the byte write
operation, once the stop condition is received an
internal write cycle will begin (Figure 4-3).
Following the start signal from the master, the slave
address (four bits), three zero bits (000) and the R/W bit
which is a logic low are placed onto the bus by the
master transmitter. This indicates to the addressed
slave receiver that a byte with a word address will follow
after it has generated an acknowledge bit during the
ninth clock cycle. Therefore, the next byte transmitted
by the master is the word address and will be written
into the address pointer of the 24LC21A. After receiving another acknowledge signal from the 24LC21A the
master device will transmit the data word to be written
into the addressed memory location. The 24LC21A
acknowledges again and the master generates a stop
condition. This initiates the internal write cycle, and
during this time the 24LC21A will not generate
acknowledge signals (Figure 4-1).
It is required that VCLK be held at a logic high level
during command and data transfer in order to program
the device. This applies to both byte write and page
write operation. Note, however, that the VCLK is
ignored during the self-timed program operation.
Changing VCLK from high to low during the self-timed
program operation will not halt programming of the
device.
It is required that VCLK be held at a logic high level
during command and data transfer in order to program
the device. This applies to both byte write and page
write operation. Note, however, that the VCLK is
ignored during the self-timed program operation.
Changing VCLK from high to low during the self-timed
program operation will not halt programming of the
device.
Note:
 1999 Microchip Technology Inc.
Page Write
Page write operations are limited to writing
bytes within a single physical page, regardless of the number of bytes actually being
written. Physical page boundaries start at
addresses that are integer multiples of the
page buffer size (or ‘page size’) and end at
addresses that are integer multiples of
[page size - 1]. If a page write command
attempts to write across a physical page
boundary, the result is that the data wraps
around to the beginning of the current page
(overwriting data previously stored there),
instead of being written to the next page as
might be expected. It is therefore necessary for the application software to prevent
page write operations that would attempt to
cross a page boundary.
DS21160E-page 9
24LC21A
FIGURE 4-1:
BYTE WRITE
S
T
A
R
T
BUS ACTIVITY
MASTER
SDA LINE
WORD
ADDRESS
CONTROL
BYTE
S
T
O
P
DATA
S
P
A
C
K
A
C
K
BUS ACTIVITY
A
C
K
VCLK
FIGURE 4-2:
VCLK WRITE ENABLE TIMING
SCL
THD:STA
SDA
IN
THD:STO
VCLK
TVHST
FIGURE 4-3:
TSPVL
PAGE WRITE
BUS ACTIVITY
MASTER
S
T
A
R
T
SDA LINE
S
BUS ACTIVITY
WORD
ADDRESS
CONTROL
BYTE
DATA n + 1
DATA (n)
S
T
O
P
DATA n + 7
P
A
C
K
A
C
K
A
C
K
A
C
K
A
C
K
VCLK
DS21160E-page 10
 1999 Microchip Technology Inc.
24LC21A
5.0
ACKNOWLEDGE POLLING
Since the device will not acknowledge during a write
cycle, this can be used to determine when the cycle is
complete (this feature can be used to maximize bus
throughput). Once the stop condition for a write
command has been issued from the master, the device
initiates the internally timed write cycle. ACK polling
can be initiated immediately. This involves the master
sending a start condition followed by the control byte for
a write command (R/W = 0). If the device is still busy
with the write cycle, then no ACK will be returned. If the
cycle is complete, then the device will return the ACK
and the master can then proceed with the next read or
write command. See Figure 5-1 for the flow diagram.
FIGURE 5-1:
6.0
WRITE PROTECTION
When using the 24LC21A in the Bi-directional Mode,
the VCLK pin can be used as a write protect control pin.
Setting VCLK high allows normal write operations,
while setting VCLK low prevents writing to any location
in the array. Connecting the VCLK pin to VSS would
allow the 24LC21A to operate as a serial ROM,
although this configuration would prevent using the
device in the Transmit-Only Mode.
ACKNOWLEDGE POLLING
FLOW
Send
Write Command
Send Stop
Condition to
Initiate Write Cycle
Send Start
Send Control Byte
with R/W = 0
Did Device
Acknowledge
(ACK = 0)?
No
Yes
Next
Operation
 1999 Microchip Technology Inc.
DS21160E-page 11
24LC21A
7.0
READ OPERATION
7.2
Random read operations allow the master to access
any memory location in a random manner. To perform
this type of read operation, first the word address must
be set. This is done by sending the word address to the
24LC21A as part of a write operation. After the word
address is sent, the master generates a start condition
following the acknowledge. This terminates the write
operation, but not before the internal address pointer is
set. Then the master issues the control byte again but
with the R/W bit set to a one. The 24LC21A will then
issue an acknowledge and transmits the 8-bit data
word. The master will not acknowledge the transfer but
does generate a stop condition and the 24LC21A
discontinues transmission (Figure 7-2).
Read operations are initiated in the same way as write
operations with the exception that the R/W bit of the
slave address is set to one. There are three basic types
of read operations: current address read, random read
and sequential read.
7.1
Current Address Read
The 24LC21A contains an address counter that
maintains the address of the last word accessed,
internally incremented by one. Therefore, if the
previous access (either a read or write operation) was
to address n, the next current address read operation
would access data from address n + 1. Upon receipt of
the slave address with R/W bit set to one, the 24LC21A
issues an acknowledge and transmits the eight bit data
word. The master will not acknowledge the transfer but
does generate a stop condition and the 24LC21A
discontinues transmission (Figure 7-1).
FIGURE 7-1:
BUS ACTIVITY
MASTER
SDA LINE
7.3
CONTROL
BYTE
S
T
O
P
DATA n
S101 00001
To provide sequential reads the 24LC21A contains an
internal address pointer which is incremented by one at
the completion of each operation. This address pointer
allows the entire memory contents to be serially read
during one operation.
P
N
O
A
C
K
A
C
K
BUS ACTIVITY
Sequential Read
Sequential reads are initiated in the same way as a
random read except that after the 24LC21A transmits
the first data byte, the master issues an acknowledge
as opposed to a stop condition in a random read. This
directs the 24LC21A to transmit the next sequentially
addressed 8-bit word (Figure 7-3).
CURRENT ADDRESS READ
S
T
A
R
T
Random Read
7.4
Noise Protection
The 24LC21A employs a VCC threshold detector circuit
which disables the internal erase/write logic if the VCC
is below 1.5 volts at nominal conditions.
The SDA, SCL and VCLK inputs have Schmitt trigger
and filter circuits which suppress noise spikes to assure
proper device operation even on a noisy bus.
FIGURE 7-2:
RANDOM READ
S
T
A
R
T
BUS ACTIVITY
MASTER
CONTROL
BYTE
WORD
ADDRESS
S 1 0 1 0 0 0 0 0
SDA LINE
CONTROL
BYTE
S
T
O
P
DATA n
S 1 0 1 0 0 0 0 1
P
A
C
K
A
C
K
A
C
K
BUS ACTIVITY
FIGURE 7-3:
S
T
A
R
T
N
O
A
C
K
SEQUENTIAL READ
BUS ACTIVITY
MASTER
DATA n
CONTROL
BYTE
DATA n+2
DATA n+1
S
T
O
P
DATA n+X
P
SDA LINE
BUS ACTIVITY
DS21160E-page 12
A
C
K
A
C
K
A
C
K
A
C
K
N
O
A
C
K
 1999 Microchip Technology Inc.
24LC21A
8.0
PIN DESCRIPTIONS
8.1
SDA
This pin is used to transfer addresses and data into and
out of the device, when the device is in the Bi-directional Mode. In the Transmit-Only Mode, which only
allows data to be read from the device, data is also
transferred on the SDA pin. This pin is an open drain
terminal, therefore the SDA bus requires a pullup
resistor to VCC (typical 10 KΩ for 100 kHz, 2 KΩ for
400 kHz).
For normal data transfer in the Bi-directional Mode,
SDA is allowed to change only during SCL low.
Changes during SCL high are reserved for indicating
the START and STOP conditions.
8.2
SCL
This pin is the clock input for the Bi-directional Mode,
and is used to synchronize data transfer to and from the
device. It is also used as the signaling input to switch
the device from the Transmit-Only Mode to the Bi-directional Mode. It must remain high for the chip to continue
operation in the Transmit-Only Mode.
8.3
VCLK
This pin is the clock input for the Transmit-Only Mode
(DDC1). In the Transmit-Only Mode, each bit is clocked
out on the rising edge of this signal. In the Bi-directional
Mode, a high logic level is required on this pin to enable
write capability.
 1999 Microchip Technology Inc.
DS21160E-page 13
24LC21A
Notes:
DS21160E-page 14
 1999 Microchip Technology Inc.
24LC21A
24LC21A Product Identification System
To order or to obtain information (e.g., on pricing or delivery), please use the listed part numbers, and refer to the factory or the listed
sales offices.
24LC21A
—
/P
Package:
Temperature
Range:
Device:
P = Plastic DIP (300 mil Body), 8-lead
SN = Plastic SOIC (150 mil Body), 8-lead
Blank =
0°C to +70°C
I = -40°C to +85°C
24LC21A
24LC21AT
Dual Mode Serial EEPROM
Dual Mode Serial EEPROM (Tape and Reel)
Sales and Support
Data Sheets
Products supported by a preliminary Data Sheet may have an errata sheet describing minor operational differences and recommended workarounds. To determine if an errata sheet exists for a particular device, please contact one of the following:
1. Your local Microchip sales office
2. The Microchip Corporate Literature Center U.S. FAX: (602) 786-7277
3. The Microchip Worldwide Site (www.microchip.com)
Please specify which device, revision of silicon and Data Sheet (include Literature #) you are using.
New Customer Notification System
Register on our web site (www.microchip.com/cn) to receive the most current information on our products.
 1999 Microchip Technology Inc.
DS21160E-page 15
WORLDWIDE SALES AND SERVICE
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ASIA/PACIFIC (continued)
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11/15/99
Microchip received QS-9000 quality system
certification for its worldwide headquarters,
design and wafer fabrication facilities in
Chandler and Tempe, Arizona in July 1999. The
Company’s quality system processes and
procedures are QS-9000 compliant for its
PICmicro® 8-bit MCUs, KEELOQ® code hopping
devices, Serial EEPROMs and microperipheral
products. In addition, Microchip’s quality
system for the design and manufacture of
development systems is ISO 9001 certified.
All rights reserved. © 1999 Microchip Technology Incorporated. Printed in the USA. 11/99
Printed on recycled paper.
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 1999 Microchip Technology Inc.