82801CA Datasheet, PDF (198/521 Pages) Intel Corporation – I/O Controller Hub 3-S (ICH3-S)

Functional Description
Read Byte/Word
Reading data is slightly more complicated than writing data. First the ICH3 must write a command
to the slave device. Then it must follow that command with a repeated start condition to denote a
read from that device's address. The slave then returns 1 or 2 bytes of data.
When programmed for the Read Byte/Word command, the Transmit Slave Address and Device
Command Registers are sent. Data is received into the data 0 on the read byte, and the Data 0 and
Data 1 Registers on the Read Word command. The Read Byte / Word command with I2C_EN set
produces undefined results. Software should force the I2C_EN bit to 0 when running this
command. The format of the protocol is shown in Table 5-82 and Table 5-83.
Table 5-82. Read Byte/Word Protocol without PEC
Read Byte Protocol
Read Word Protocol
Bit
1
2–8
9
10
11–18
19
20
21–27
28
29
30–37
38
39
Description
Start
Slave Address–7 bits
Write
Acknowledge from slave
Command code–8 bits
Acknowledge from slave
Repeated Start
Slave Address–7 bits
Read
Acknowledge from slave
Data from slave–8 bits
NOT acknowledge
Stop
Bit
1
2–8
9
10
11–18
19
20
21–27
28
29
30–37
38
39–46
47
48
Description
Start
Slave Address–7 bits
Write
Acknowledge from slave
Command code–8 bits
Acknowledge from slave
Repeated Start
Slave Address–7 bits
Read
Acknowledge from slave
Data Byte Low from slave–8 bits
Acknowledge
Data Byte High from slave–8 bits
NOT acknowledge
Stop
198
Intel^® 82801CA ICH3-S Datasheet