BUS Specification

UNI/O®
Bus Specification
© 2009 Microchip Technology Inc.
DS22076D
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rfPIC and UNI/O are registered trademarks of Microchip
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Printed on recycled paper.
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and manufacture of development systems is ISO 9001:2000 certified.
DS22076D-page 2
© 2009 Microchip Technology Inc.
UNI/O® Bus
Table of Contents
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
Introduction ............................................................................................................................................................ 5
General Characteristics ......................................................................................................................................... 8
Standby Pulse ....................................................................................................................................................... 9
Bit-Level Definition .............................................................................................................................................. 10
Byte-Level Definition ........................................................................................................................................... 11
Start Header ........................................................................................................................................................ 12
8-Bit Device Addressing ...................................................................................................................................... 13
12-Bit Device Addressing .................................................................................................................................... 14
Command Structure ............................................................................................................................................ 15
Device Address Polling ....................................................................................................................................... 16
Device Modes ...................................................................................................................................................... 17
Electrical Specifications ....................................................................................................................................... 18
© 2009 Microchip Technology Inc.
DS22076D-page 3
UNI/O® Bus
NOTES:
DS22076D-page 4
© 2009 Microchip Technology Inc.
UNI/O® Bus
UNI/O® Bus Specification
1.0
INTRODUCTION
One device is defined as the master and is responsible
for initiating and coordinating all operations with the
slave devices on the bus. Each slave acts as a peripheral to the master and a slave can be designed for any
number of purposes.
As embedded systems become smaller, there exists a
growing need to minimize I/O signal consumption for
communication between devices. Microchip has
addressed this need by developing the patented**
UNI/O® bus, a low-cost, easy-to-implement solution
requiring only a single I/O signal for communication.
Figure 1-1 shows an example system with a microcontroller acting as the master, and other numerous
devices attached to the bus as slave peripherals. Note
that the master is not limited to being a microcontroller,
but can be any device capable of processing the
necessary I/O signal.
UNI/O bus-compatible devices can be used to enhance
any application facing restrictions on available I/O.
Such restrictions can possibly stem from connectors,
board space, or from the master device itself.
1.1
Data is embedded into the I/O stream through
Manchester encoding. The bus is controlled by the
master which determines the clock period, controls the
bus access and initiates all operations, while all other
devices act as slaves. Both master and slave devices
can operate as transmitter or receiver, but the master
determines which mode is active.
Description
The UNI/O bus provides the definition for communication through a single I/O signal. It supports the use of
multiple devices through a “bussed” system.
The UNI/O bus supports operation from 10 kbps to 100
kbps (equivalent to 10 kHz to 100 kHz) and places no
restrictions on voltage ranges, temperature ranges, or
manufacturing processes.
FIGURE 1-1:
UNI/O® BUS EXAMPLE
Microcontroller
Serial
EEPROM
Temperature
Sensor
Digital
Potentiometer
(Master)
(Slave)
(Slave)
(Slave)
SCIO
A/D
Converter
Programmable
Gain Amplifier
I/O Port
Expander
(Slave)
(Slave)
(Slave)
**UNI/O® is a registered trademark of Microchip Technology Inc. Microchip’s UNI/O Bus products are covered by the
following patent issued in the U.S.A.: 7,376,020.
© 2009 Microchip Technology Inc.
DS22076D-page 5
UNI/O® Bus
1.2
1.2.1
Definitions
SCIO
SCIO is the only I/O signal required for the UNI/O bus.
Both the serial clock and data are embedded together
through Manchester encoding. In this encoding
method, each bit consists of a mandatory edge in the
middle of a bit period. The direction of this edge determines the value of the bit. A rising edge indicates a ‘1’,
whereas a falling edge indicates a ‘0’.
1.2.2
MASTER DEVICE
The master device determines the clock period, controls bus access and initiates all operations. Only one
master is allowed in a system. Examples of master
devices include microcontrollers, ASICs and FPGAs.
1.2.3
SLAVE DEVICE
A slave device acts as a peripheral on the bus. Slaves
do not initiate any operations; they merely respond to
operations begun by the master. Each slave must
have a unique device address with which the master
can select the device. Slave devices can operate as
both transmitter and receiver, but the mode is determined by the master in conjunction with the command
issued. Examples of slave devices include serial
EEPROMs, temperature sensors and A/D converters.
1.2.4
TRANSMITTER
The transmitter is defined as the device with control of
the bus during transmission of a byte. For example,
while data is outputting from a slave to the master, the
slave is acting as the transmitter.
1.2.5
RECEIVER
1.2.8
START HEADER
The start header is the combination of a short low
pulse followed by a header byte of the value
‘01010101’. This is always the first byte transmitted
for any given command.
After the header byte has been sent, an Acknowledge
sequence is performed. For this specific sequence
only, no slave responds during the normal SAK time.
1.2.9
DEVICE ADDRESS
Following the start header, the device address is sent.
This can consist of either one or two bytes, depending
on whether 8-bit or 12-bit device addressing is supported, respectively. The purpose of the device
address is to select a specific slave device on the bus.
For this reason, every slave device in a system must
have a unique device address. Otherwise, bus
conflicts will occur and operation will be undefined.
1.2.10
FAMILY CODE
The family code is a 4-bit value included in the device
address and indicates the family in which the device
resides. Examples of device families include memory
devices, temperature sensors and A/D converters.
1.2.11
DEVICE CODE
The device code is either a 4- or 8-bit value, depending on whether 8-bit or 12-bit device addressing is
supported, respectively. It is used to differentiate
devices with the same family code. Some devices may
support programmable device code bits, whereas on
others they may be fixed.
1.2.12
ACKNOWLEDGE SEQUENCE
The receiver is defined as the device receiving the
current byte of data. For example, while a command is
being transmitted to a slave from the master, the slave
is acting as the receiver.
After each byte is transmitted, a 2-bit Acknowledge
sequence is performed. The first bit is for the MAK and
the second bit is for the SAK. The sequence is used to
indicate continuation or termination of an operation, as
well as to confirm reception of a byte.
1.2.6
1.2.13
BIT PERIOD
The bit period is defined as the amount of time
reserved for transmission of a single bit. This time
period is determined by the master. All slaves recover
this period through the start header by measuring the
amount of time needed to send the header.
For each bit, the Manchester-encoded bit edge must
occur at the middle of the bit period.
1.2.7
STANDBY PULSE
The high pulse used to place all slave devices into
Standby mode is called the standby pulse. It is
required at the beginning of a command when selecting a new device.
DS22076D-page 6
MAK/NOMAK
The MAK bit occurs as the first bit of every Acknowledge sequence. It is always sent by the master,
regardless of which device transmitted the preceding
byte. A MAK is sent as a ‘1’, and a NoMAK as a ‘0’.
Sending a MAK during an Acknowledge sequence
indicates that the current operation is to be continued.
This means that more data is to be sent by the device
acting as transmitter. A NoMAK indicates that the
current operation is to be terminated immediately
following the Acknowledge sequence.
© 2009 Microchip Technology Inc.
UNI/O® Bus
1.2.14
SAK/NOSAK
The SAK bit occurs as the second bit of the Acknowledge sequence and is sent strictly by the slave device
regardless of which device transmitted the preceding
byte. A SAK is sent as a ‘1’, and a NoSAK appears as
no edge at all (i.e., no device transmitting).
A NoSAK will occur after each full byte that is transmitted before the end of the device address. For example, for 8-bit addressing, a NoSAK will occur after the
start header only, and for 12-bit addressing, a NoSAK
will occur after both the start header and the MSB of
the device address.
1.2.15
IDLE MODE
Idle mode is a device mode during which a slave device
ignores all serial communication until the reception of a
standby pulse. Slave devices enter this mode after
release from POR, as well as any time an error
condition occurs.
1.2.16
STANDBY MODE
Standby mode is a low-power device mode during
which a slave device awaits a high-to-low transition on
SCIO, marking the beginning of the start header. Slave
devices enter this mode upon reception of a standby
pulse and after the successful termination of a
command via a NoMAK/SAK combination.
1.2.17
HOLD MODE
Hold provides a method for the master to pause serial
communication in order to service interrupts or perform
other necessary functions. Hold mode is entered by
holding SCIO low during any given MAK bit period and
is exited by performing a standard Acknowledge
sequence with a MAK bit.
Hold mode is not required to be implemented on all
slave devices.
© 2009 Microchip Technology Inc.
DS22076D-page 7
UNI/O® Bus
2.0
GENERAL CHARACTERISTICS
2.4
Bus Capacitance
There is only a single I/O signal, SCIO, necessary for
communication between devices and all data transmission occurs through this line. The SCIO signal for
all devices in a system are connected together directly
in a bussed configuration. The Idle state of the bus is
high. In order to ensure the bus is in the Idle state during times when the master may not be driving the bus,
the use of a pull-up resistor is recommended. Both
clock and data are embedded together by way of
Manchester encoding.
Successful communication is dependant upon edge
transitions occurring within the proper time frames.
Moreover, slew rates must be minimized to avoid
detecting unwanted edges, most critically during the
start header. Because of this, the bus capacitance is
limited to 100 pF. This is comprised of the SCIO pin
capacitance for all devices on the bus, as well as the
capacitance of all wires and connections.
The serial stream is divided into bit periods, with one
data bit being embedded per period. The bit period
time is determined by the master and communicated
to the slave during the start header at the beginning of
each command. Therefore, the bit period must only be
consistent within a single command.
The UNI/O bus is not designed for any particular process or technology. Therefore, all IC fabrication technologies are supported, so long as the electrical
specifications set forth in Section 12.0 “Electrical
Specifications” are met.
2.1
2.5
Fabrication Processes
Bit Rate
Parameter FBIT in Table 12-2 defines the currently
supported frequency range. Note that, due to the
asynchronous nature of the bus, both minimum and
maximum frequencies are defined.
2.2
Voltage Range
In order to support a wide number of fabrication processes, no limitation has been defined for the operating voltages of devices attached to the bus. Such
ranges are dependent solely on the specific devices.
The only requirement is that input threshold voltages
and output current limits meet the electrical specifications set forth in Table 12-1.
2.3
I/O Structures
The I/O structure for SCIO consists of an input buffer
and a tri-stateable, push-pull output driver. To avoid
high currents during possible bus contention, and to
refrain from requiring external components, the SCIO
output driver on all slave devices must be current-limited to the specifications listed in Table 12-1. If the output driver on the master device in a system is not
significantly stronger than on the slave devices,
ambiguous voltage levels may occur during times of
possible bus contention.
Because the bus Idle state is high, a pull-up resistor is
recommended to ensure bus idle during power
up/down sequences, as well as any other time in
which no device is driving the bus.
DS22076D-page 8
© 2009 Microchip Technology Inc.
UNI/O® Bus
STANDBY PULSE
If a command is terminated in any manner other than a
NoMAK/SAK combination, or if an invalid number of
data bytes has been sent (as specified by the command’s definition), then this is considered an error
condition and the master must perform a standby
pulse before beginning a new command, regardless of
which device is to be selected.
Before communicating with a new device, a standby
pulse must be performed. This pulse signals to all
slave devices on the bus to enter Standby mode,
awaiting a new command to begin. The standby pulse
can also be used to prematurely terminate a
command.
An example of two consecutive commands is shown in
Figure 3-1. Note that the device address is the same
for both commands, indicating that the same device is
being selected both times.
The standby pulse consists of holding SCIO high for a
minimum of TSTBY. After this has been performed, the
slave devices will be ready to receive a command.
Once a command is terminated satisfactorily (i.e., via
a NoMAK/SAK combination during the Acknowledge
sequence), performing a standby pulse is not required
to begin a new command as long as the device to be
selected is the same device selected during the previous command. In this case, a period of TSS must be
observed after the end of the command and before the
beginning of the start header. After TSS, the start
header (including low pulse) can be transmitted in
order to begin the new command.
CONSECUTIVE COMMANDS EXAMPLE
Standby Pulse
Start Header
MAK
SAK
FIGURE 3-1:
Note: After a POR/BOR event occurs, a lowto-high transition on SCIO must be generated before proceeding with any communication, including a standby pulse.
MAK
NoSAK
3.0
Device Address
SCIO
1 0 1 0 0 0 0 0
Device Address
MAK
SAK
Start Header
MAK
NoSAK
NoMAK
SAK
TSS
0 1 0 1 0 1 0 1
SCIO
0 1 0 1 0 1 0 1
1 0 1 0 0 0 0 0
Upon detection of the standby pulse, a slave device
will typically enter its lowest power state. The exception to this is when the slave device is executing an
internal process in the background. Examples include
an EEPROM performing a write cycle, or a temperature sensor carrying out a conversion.
If at any point during a command an error is detected
by the master, a standby pulse should be generated
and the command should be performed again.
© 2009 Microchip Technology Inc.
DS22076D-page 9
UNI/O® Bus
4.0
BIT-LEVEL DEFINITION
FIGURE 4-2:
Clock and data are embedded together through Manchester encoding. Each data bit is transmitted within a
single bit period, TE, which is specified by the master
during the start header of the command.
SUCCESSIVE BIT
TRANSMISSION
EXAMPLE
‘1’
‘1’
Every bit period includes an edge transition at the middle of the period, and it is the direction of this edge
which determines the value of the bit. A rising middle
edge indicates a ‘1’ value, whereas a falling edge
indicates a ‘0’, as shown in Figure 4-1.
FIGURE 4-1:
‘1’
BIT VALUES
Edge Exists
‘0’
‘1’
TE
‘0’
TE
Because every bit period must have a middle edge
transition, there may or may not exist another edge
transition at the beginning of a bit period. This is
entirely dependent upon the values of both the previous and current bits. If two bits of equal value are
being successively transmitted, then a transition at the
beginning of the second bit is required. If the two bits
are of opposing values, then no edge will occur. Refer
to Figure 4-2 for details.
No Edge Exists
4.1
Timing Considerations
In order to allow for flexibility in timing, UNI/O buscompatible devices must be tolerant of small deviations, or jitter, in input edge timing, as specified by
TIJIT. See Figure 12-4 for details.
Slave devices must also allow for a small amount of
frequency drift. FDRIFT specifies the maximum drift per
byte tolerance required for all slave devices, and FDEV
shows the overall drift from the initial serial bit period
for a single command. For example, if a command is
begun using a 20 µs bit period, the master can drift a
maximum of 20 µs*FDRIFT per byte, up to a total of 20
µs*FDEV within that command.
DS22076D-page 10
© 2009 Microchip Technology Inc.
UNI/O® Bus
5.0
BYTE-LEVEL DEFINITION
Communication is formatted using 8-bit bytes. All
bytes are transmitted with the Most Significant bit sent
first and the Least Significant bit sent last. Each bit is
transmitted immediately following the previous bit, with
no delay in between bits. An example is shown in
Figure 5-1.
FIGURE 5-1:
BYTE TRANSMISSION EXAMPLE
‘1’
‘0’
‘1’
‘1’
‘0’
‘1’
‘0’
‘0’
SCIO
5.1
Acknowledge Sequence
An Acknowledge routine occurs after each byte is
transmitted, including the start header. This routine
consists of two bits. The first bit is transmitted by the
master and the second bit is transmitted by the slave,
as shown in Figure 5-2.
5.1.3
ERROR DETECTION
If a SAK is not received from the slave after any byte
(after a device has been selected), an error has
occurred. The master should then perform a standby
pulse and begin the desired command again.
FIGURE 5-2:
5.1.1
MAK
The Master Acknowledge, or MAK, is signified by transmitting a ‘1’ and informs the slave that the command is
to be continued (i.e., more data will be sent).
Conversely, a Not Acknowledge, or NoMAK, is signified
by transmitting a ‘0’, as shown in Figure 5-3, and is
used to end the current command and initiate any
corresponding internal processing, if necessary.
A MAK must always be transmitted following the start
header. If a NoMAK is transmitted, device operation will
be undefined.
5.1.2
ACKNOWLEDGE
ROUTINE
Master
Slave
MAK
SAK
FIGURE 5-3:
ACKNOWLEDGE BITS
MAK (‘1’)
SAK (‘1’)
NoMAK (‘0’)
NoSAK(1)
SAK
The Slave Acknowledge, or SAK, is also signified by
transmitting a ‘1’ and confirms successful reception of
the previous byte of data. Unlike the NoMAK, the
NoSAK is signified by the lack of a middle edge during
the bit period.
In order to avoid possible bus collision due to multiple
devices transmitting at the same time, no slave device
will respond with a SAK until a specific slave has been
selected. That is, a NoSAK will occur after each byte
that is transmitted before the end of the device address
(i.e., for 8-bit addressing, a NoSAK occurs after the
start header only, and for 12-bit addressing, a NoSAK
occurs after both the start header and the MSB of the
device address).
© 2009 Microchip Technology Inc.
Note 1:
A NoSAK is defined as any sequence that is not a
valid SAK.
DS22076D-page 11
UNI/O® Bus
6.0
START HEADER
When a standby pulse is not required (i.e., between
successive commands to the same device), a period
of TSS must be observed after the end of the command
and before the beginning of the start header.
All operations must be preceded by a start header.
The start header consists of holding SCIO low for a
period of THDR, followed by transmitting an 8-bit
‘01010101’ code. This code is used to synchronize
the slave’s internal clock period with the master’s clock
period, so accurate timing is very important. An
Acknowledge sequence is then performed following
transmission of the start header. Figure 6-1 shows an
example of the start header sequence.
FIGURE 6-1:
TSS
START HEADER EXAMPLE
THDR
‘0’
‘1’
‘0’
‘1’
‘0’
‘1’
‘0’
‘1’
MAK
NoSAK
SCIO
Synchronization
During the Acknowledge sequence following the start
header, no slave device will respond with a SAK.
Within this time, the bus will not be driven by any
device and no edge transition will occur. Refer to
Section 5.1 “Acknowledge Sequence” for details.
6.1
6.1.1
Synchronization
OSCILLATOR
In order to provide an accurate time base with which to
extract the serial clock frequency, an oscillator must be
used by each slave device on the bus. This can be
either internal or external to the device, though including an internal oscillator is strongly recommended to
avoid requiring excess external components.
The necessary accuracy of the oscillator to a specific
frequency is dependent only on the design of the
device. The only bus-based requirements are that the
chosen oscillator be stable enough across voltage and
temperature and that the frequency is high enough to
provide a reasonable state of synchronization during a
command.
If an internal oscillator is included, it is recommended
that it be powered down during Idle and Standby
modes so as to reduce unnecessary power consumption. The THDR period provides a time during which
such an internal oscillator can power-up and stabilize.
6.1.2
SERIAL FREQUENCY EXTRACTION
The start header is utilized by slave devices as a
means of determining the bit period used by the master. During the start header, a counter can be used to
measure the amount of time required to transmit 8 bits
of data. This counter can then be divided down to
determine the bit period, TE, which can be used as a
comparison for all other bits.
The required widths of such counters are dependent
upon the oscillator frequency used and would need to
be wide enough to support 100 µs bit periods (10 kbps
operation).
6.2
Re-synchronization
During communication, it is possible that either the
master’s or the slave’s reference clock may drift. This
may be due to many events, including changes in voltage or temperature. If not corrected for, such a drift will
eventually cause a loss of synchronization. Therefore,
all slave devices must monitor the middle edge of
each MAK bit and where it occurs relative to the
slave’s bit period, and then adjust its frequency to
match.
6.2.1
PHASE ADJUSTMENT
During every MAK bit, the middle edge should also be
used to reset the slave’s phase (i.e., the slave should
assume that the MAK edge is located at the middle of
the master’s bit period and therefore use it as a
reference for further communication).
This will ensure that any error in phase which may
occur will not accumulate from byte to byte.
DS22076D-page 12
© 2009 Microchip Technology Inc.
UNI/O® Bus
7.0
8-BIT DEVICE ADDRESSING
In order to differentiate individual slave devices on the
bus, a device address byte is sent by the master
device following the start header. This is an 8-bit value
used to select a specific device attached to the bus.
The device address byte consists of a 4-bit family code
and a 4-bit device code. The device code may be
either fixed or programmable in order to provide the
ability to cascade multiple devices with identical family
codes on the same bus.
FIGURE 7-1:
8-BIT DEVICE ADDRESS
DEVICE ADDRESS
Family Code
A7
7.1
A6
A5
7.2
Device Code
The lower nibble (bits A3-A0) of the device address is
the device code. This code is a 4-bit value and is used
to differentiate between multiple devices on the bus
within the same family. The device code is defined at
the device level and can be either fixed or customizable. Such customizable bits can be implemented in
any manner, including via external input pins or
software configuration.
It is strongly recommended that as many customizable
device code bits as possible be included in order to
help avoid address conflicts.
MAK SAK
Device Code
A4
A3
A2
A1
A0
Family Code
The upper nibble (bits A7-A4) of the device address is
the family code. This code is a 4-bit value and specifies in which family the device resides. The families
and codes are defined by Microchip and must be followed in order to reduce the risk of address conflicts.
To obtain the proper code for a specific device, please
contact Microchip.
Certain codes have been reserved for special
functions and are listed in Table 7-1.
TABLE 7-1:
RESERVED FAMILY CODES
Code
Description
‘0000’ Reserved for future use
‘0011’ Display Controllers
‘0100’ I/O Port Expanders
‘1000’ Frequency/Quadrature/PWM Encoders,
Real-Time Clocks
‘1001’ Temperature Sensors
‘1010’ EEPROMs
‘1011’ Encryption/Authentication Devices
‘1100’ DC/DC Converters
‘1101’ A/D Converters
‘1111’ 12-bit Addressable Devices
© 2009 Microchip Technology Inc.
DS22076D-page 13
UNI/O® Bus
8.0
12-BIT DEVICE ADDRESSING
The 12-bit device addressing scheme takes advantage of the ‘1111’ family code defined in Section 7.1
“Family Code”. This code functions as an enable for
12-bit addressing compatible devices and will place all
other devices into Idle mode.
As an extension to 8-bit device addressing (Section
7.0 “8-Bit Device Addressing”), 12-bit device
addressing allows for support of a much larger number
of devices. Devices designed to support 12-bit
addressing are fully compatible with 8-bit addressable
devices, and both can be connected onto the bus
concurrently.
FIGURE 8-1:
12-BIT DEVICE ADDRESS
DEVICE HIGH ADDRESS
8.1
1
1
1
No
SAK
DEVICE LOW ADDRESS
Family Code
12-Bit Address Code
1
MAK
A11
A10
A9
MAK SAK
Device Code
A8
A7
A6
A5
A4
A3
A2
A1
A0
Family Code
The lower nibble (bits A11-A8) of the device high
address is the family code. This code is a 4-bit value
and specifies in which family the device resides. The
families and codes are defined by Microchip and must
be followed in order to reduce the risk of address conflicts. To obtain the proper code for a specific device,
please contact Microchip.
Certain codes have been reserved for special
functions and are listed in Table 8-1.
TABLE 8-1:
Code
FAMILY CODES
Description
‘0000’ Reserved for future use
‘1111’ Reserved for future use
8.2
Device Code
The low byte (bits A7-A0) of the device address is the
device code. This code is an 8-bit value and is used to
differentiate between multiple devices on the bus
within the same family. The device code is defined at
the device level and can be either fixed or customizable. Such customizable bits can be implemented in
any manner, including via external input pins or
software configuration.
It is strongly recommended that as many customizable
device code bits as possible be included in order to
help avoid address conflicts.
DS22076D-page 14
© 2009 Microchip Technology Inc.
UNI/O® Bus
COMMAND STRUCTURE
A full operation consists of the following steps:
•
•
•
•
•
After the device address, a command byte must be
sent by the master to indicate the type of operation to
be performed. This command is defined at the device
level and no restrictions are placed on it by the bus.
A full operation can consist of any number of bytes,
ranging from a single command byte to a theoretically
unlimited maximum. After the initial command byte,
additional bytes can be included for any necessary
purpose, such as for addressing or data.
Regardless of the number of bytes required, all commands are terminated through the transmission of a
NoMAK from the master.
Note 1: A standby pulse may not be required for
consecutive commands to the same
device. Refer to Section 3.0 “Standby
Pulse” for more details.
Figure 9-1 shows an example read operation for a
serial EEPROM.
Standby Pulse
Start Header
MAK
SAK
EXAMPLE EEPROM READ OPERATION
Device Address
SCIO
A3 A2 A1 A0
Word Address MSB
1 0 1 0
MAK
SAK
Command
MAK
SAK
0 1 0 1 0 1 0 1
7 6 5 4 3 2 1 0
15 14 13 12 11 10 9 8
SCIO
Word Address LSB
MAK
SAK
FIGURE 9-1:
Standby Pulse(1)
Start Header
Device Address
Command Byte
Any other bytes necessary for the operation
MAK
NoSAK
9.0
SCIO
7 6 5 4 3 2 1 0
© 2009 Microchip Technology Inc.
7 6 5 4 3 2 1 0
NoMAK
SAK
Data Byte 2
MAK
SAK
Data Byte 1
MAK
SAK
0 0 0 0 0 0 1 1
Data Byte n
7 6 5 4 3 2 1 0
DS22076D-page 15
UNI/O® Bus
DEVICE ADDRESS POLLING
Slave devices must respond with a SAK if either a MAK
or NoMAK is received following the device address, as
long as the address is valid. In the case of a NoMAK,
the slave device will return to Standby mode immediately following the transmission of the SAK.
This feature allows the master to perform an address
polling sequence in order to determine what devices
are connected to the bus. Such a sequence is typically
used in conjunction with a list of expected device
addresses to allow for added flexibility in system
design.
Figure 10-1 shows an example of polling for two
devices, both with 8-bit device addresses. In this example, the first device exists on the bus and the second
device does not exist. For 12-bit addressing, the
sequence is the same except that the SAK is checked
following the device low address.
DEVICE ADDRESS POLLING EXAMPLE
Standby Pulse
Start Header
Device Address 1
NoMAK
SAK
FIGURE 10-1:
In order to perform device address polling, the master
generates a standby pulse and start header and transmits the desired device address followed by a NoMAK.
The master then checks to see whether or not a corresponding slave transmits a SAK. If a SAK is received,
then a slave exists with the specified device address.
Note that a standby pulse must be generated before
every command, as a different device is being
addressed during each sequence.
MAK
NoSAK
10.0
SCIO
Start Header
Device Address 2
NoMAK
NoSAK
Standby Pulse
1 0 1 0 0 0 0 0
MAK
NoSAK
0 1 0 1 0 1 0 1
SCIO
0 1 0 1 0 1 0 1
DS22076D-page 16
1 0 1 0 0 0 0 1
© 2009 Microchip Technology Inc.
UNI/O® Bus
11.0
DEVICE MODES
11.1
Device Idle
11.3
Slave devices must feature a Idle mode during which
all serial data is ignored until a standby pulse occurs.
Idle mode will be entered, without generation of a
SAK, upon the following conditions:
• Invalid Device Address
• Invalid command byte
• Missed edge transition (except when entering
Hold)
• Reception of a NoMAK before completing a
command sequence, except following a
device address
An invalid start header cannot be detected, but will
indirectly also cause the device to enter Idle mode by
preventing the slave from synchronizing properly with
the master. If the slave is not synchronized with the
master, an edge transition will be missed, thus causing
the device to enter Idle mode.
11.2
Device Standby
Slave devices must feature a Standby mode during
which the device is waiting to begin a new command.
After observing the TSS time period, a high-to-low transition on SCIO will exit Standby and prepare the
device for reception of the start header.
Device Hold
Hold mode allows the master to suspend communication in order to perform other tasks, such as servicing
interrupts, etc. In order to initiate the Hold sequence,
the master must bring SCIO low at the beginning of
the next MAK bit period for a minimum time of THLD
and continue to keep it low while in hold.
To bring the slave out of hold, the master continues the
current operation, starting with an Acknowledge
sequence as described in Section 5.1 “Acknowledge
Sequence”, transmitting a MAK and checking for the
slave response. See Figure 11-1 for more details. The
Acknowledge sequence need not be in phase with
previously transmitted bits, thereby allowing the Hold
sequence to last for any length of time greater than
THLD. The bit period must remain constant throughout
the hold sequence.
Note that if SCIO is held low for a full bit period (i.e., if
a middle edge does not occur) at any point other than
a MAK, the slave must consider this an error condition,
terminate the operation and enter Idle mode.
A Hold sequence must be terminated by issuing a
MAK. If a NoMAK is issued, there is no method for
detecting this, and the operation will be undefined.
Implementation of the Hold feature is optional. Without
it, a device may still conform to the UNI/O bus
specifications.
Standby mode will be entered upon the following
conditions:
• A NoMAK followed by a SAK (i.e., valid termination of a command)
• Reception of a standby pulse
Standby mode can be used to provide a low-power
mode of operation. In order to maximize power efficiency, such a mode should be interrupted only at the
beginning of the low pulse of the start header.
Data Byte n+1
7 6 5 4 3 2 1 0
7 6 5 4 3 2 1 0
THLD
SCIO
Hold In Progress
MAK
SAK
Data Byte n
MAK
SAK
HOLD SEQUENCE
Hold Initiated
FIGURE 11-1:
© 2009 Microchip Technology Inc.
DS22076D-page 17
UNI/O® Bus
12.0
ELECTRICAL SPECIFICATIONS
TABLE 12-1:
I/O STRUCTURE DC CHARACTERISTICS
DC CHARACTERISTICS
Param.
No.
Sym.
D1
VIH
D2
VIL
D3
VHYS
D4
Min.
Max.
Units
High-level input
voltage
.7 VCC
VCC+1
V
Low-level input
voltage
-0.3
-0.3
0.3*VCC
0.2*VCC
V
VCC ≥ 2.5V
VCC < 2.5V
Hysteresis of Schmitt
Trigger inputs (SCIO)
0.05*Vcc
—
V
VCC ≥ 2.5V
VOH
High-level output
voltage
VCC -0.5
VCC -0.5
—
—
V
V
IOH = -300 μA, VCC ≥ 2.5V
IOH = -200 μA, VCC < 2.5V
D5
VOL
Low-level output
voltage
—
—
0.4
0.4
V
V
IOI = 300 μA, VCC ≥ 2.5V
IOI = 200 μA, VCC < 2.5V
D6
IO
Slave output current
limit (Note 1)
—
—
±4
±3
mA
mA
VCC ≥ 2.5V
VCC < 2.5V
D7
ILI
Input leakage current
(SCIO)
—
±10
μA
VIN = VSS or VCC
D8
CINT
Device Capacitance
(SCIO)
—
7
pF
—
D9
CB
Bus Capacitance
—
100
pF
—
Note 1:
Characteristic
Test Conditions
The slave SCIO output driver impedance must vary to ensure Io is not exceeded.
TABLE 12-2:
AC CHARACTERISTICS
AC CHARACTERISTICS
Param.
No.
Sym.
1
FBIT
2
TE
3
TIJIT
4
Characteristic
Min.
Max.
Units
Conditions
Serial Bit Frequency
10
100
kHz
—
Bit period
10
100
µs
—
Input edge jitter tolerance
—
±0.08
UI
(Note 1)
—
±0.75
%
Per byte
—
±5
%
Per command
FDRIFT Serial bit frequency drift rate
tolerance
5
FDEV
6
TR
SCIO input rise time
—
100
ns
—
7
TF
SCIO input fall time
—
100
ns
—
8
TSTBY
Standby pulse time
600
—
µs
—
9
TSS
Start header setup time
10
—
µs
—
10
THDR
11
TSP
12
THLD
Note 1:
Serial bit frequency drift limit
Start header low pulse time
5
—
µs
—
Input filter spike suppression
(SCIO)
—
50
ns
—
1*TE
—
µs
—
Hold time
A Unit Interval (UI) is equal to 1-bit period (TE) at the current bus frequency.
DS22076D-page 18
© 2009 Microchip Technology Inc.
UNI/O® Bus
FIGURE 12-1:
9
BUS TIMING – START HEADER
10
2
SCIO
Data ‘0’ Data ‘1’ Data ‘0’ Data ‘1’ Data ‘0’ Data ‘1’ Data ‘0’ Data ‘1’ MAK bit NoSAK bit
FIGURE 12-2:
BUS TIMING – DATA
2
7
Data ‘1’
Data ‘0’
11
SCIO
Data ‘0’
FIGURE 12-3:
6
Data ‘1’
BUS TIMING – STANDBY PULSE
8
SCIO
Standby
Mode
POR
Release
from POR
BUS TIMING – JITTER
2
3
Ideal Edge
Hold In Progress
MAK
SAK
Data Byte n
SCIO
Ideal Edge
HOLD SEQUENCE
Hold Initiated
FIGURE 12-5:
3
MAK
SAK
FIGURE 12-4:
Data Byte n+1
7 6 5 4 3 2 1 0
7 6 5 4 3 2 1 0
12
© 2009 Microchip Technology Inc.
DS22076D-page 19
UNI/O® Bus
NOTES:
DS22076D-page 20
© 2009 Microchip Technology Inc.
UNI/O®Bus
NOTES:
© 2009 Microchip Technology Inc.
DS22076D-page 21
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DS22076D-page 22
© 2009 Microchip Technology Inc.
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