TC654 datasheet(16/36 Pages) MICROCHIP

16 / 36 page

TC654/TC655

DS21734A-page 16

 2002 Microchip Technology Inc.

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.

FIGURE 5-1:

SMBus Protocol: Write Byte Format.

FIGURE 5-2:

SMBus Protocol: Read Byte Format.

FIGURE 5-3:

SMBus Protocol: Receive Byte Format.

ADDRESS

ACK

COMMAND

ACK

DATA

ACK

7 Bits

8 Bits

Slave Address

Command Byte: selects

which register you are

writing to.

Data Byte: data goes

into the register set

by the command byte.

ADDRESS

ACK

COMMAND

ACK

7 Bits

8 Bits

Slave Address

Command Byte: selects

which register you are

writing to.

ADDRESS

ACK

DATA

NACK

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.

ADDRESS

ACK

DATA

NACK

7 Bits

8 Bits

Slave Address

Data Byte: reads data from

the register commanded by

the last Read Byte or Write

Byte transmission

S = Start Condition

P = Stop Condition

Shaded = Slave Transmission

ACK = Acknowledge = 0

NACK = Not Acknowledged = 1

WR = Write = 0

RD = Read = 1

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