TC654(2002) データシートの表示（PDF） - Microchip Technology
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TC654 Datasheet PDF : 36 Pages
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TC654/TC655
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. 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 unlimited.
5.1.7 ACKNOWLEDGE (ACK)
Each receiving device, when addressed, is obliged to
generate an acknowledge bit after the reception of
each byte. The master device must generate an extra
clock pulse, which is associated with this acknowledge
bit.
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. Setup
and hold times must be taken into account. During
reads, a master device 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 (TC654/TC655) will leave the data line
HIGH to enable the master device to generate the
STOP condition.
5.2 SMBus Protocols
The TC654/TC655 devices communicate with three
standard SMBus protocols. These are the write byte,
read byte and receive byte. The receive byte is a short-
ened method for reading from, or writing to, a register
which had been selected by the previous read or write
command. These transmission protocols are shown in
Figures 5-1, 5-2 and 5-3.
S
ADDRESS
WR
ACK
COMMAND
ACK
7 Bits
8 Bits
Slave Address
Command Byte: selects
which register you are
writing to.
FIGURE 5-1:
SMBus Protocol: Write Byte Format.
DATA
ACK
P
8 Bits
Data Byte: data goes
into the register set
by the command byte.
S
ADDRESS
WR
ACK
COMMAND
ACK
7 Bits
8 Bits
Slave Address
Command Byte: selects
which register you are
writing to.
S
ADDRESS
RD
ACK
DATA
NACK
P
7 Bits
8 Bits
Slave Address:
repeated due to change
in data flow direction.
Data Byte: reads from
the register set by the
command byte.
FIGURE 5-2:
SMBus Protocol: Read Byte Format.
S
ADDRESS
RD
ACK
DATA
NACK
P
7 Bits
8 Bits
Slave Address
Data Byte: reads data from
the register commanded by
the last Read Byte or Write
Byte transmission
FIGURE 5-3:
SMBus Protocol: Receive Byte Format.
S = Start Condition
P = Stop Condition
Shaded = Slave Transmission
ACK = Acknowledge = 0
NACK = Not Acknowledged = 1
WR = Write = 0
RD = Read = 1
DS21734A-page 16
2002 Microchip Technology Inc.
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