82801BA Datasheet, PDF (194/498 Pages) Intel Corporation – Intel 82801BA I/O Controller Hub 2 (ICH2) and Intel 82801BAM I/O Controller Hub 2 Mobile

Functional Description
Table 5-78. Write Byte/Word Protocol
Write Byte Protocol
Bit
1
2:8
9
10
11:18
19
20:27
28
29
Description
Start
Slave Address - 7 bits
Write
Acknowledge from slave
Command code - 8 bits
Acknowledge from slave
Data Byte - 8 bits
Acknowledge from Slave
Stop
Bit
1
2:8
9
10
11:18
19
20:27
28
29:36
37
38
Write Word Protocol
Description
Start
Slave Address - 7 bits
Write
Acknowledge from slave
Command code - 8 bits
Acknowledge from slave
Data Byte Low - 8 bits
Acknowledge from Slave
Data Byte High - 8 bits
Acknowledge from slave
Stop
Read Byte/Word
Reading data is slightly more complicated than writing data. First the ICH2 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 DATA0 on the read byte, and the DAT0 and
DATA1 registers on the read word. The format of the protocol is shown in Table 5-79.
Table 5-79. Read Byte/Word Protocol
Read Byte 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
Read Word Protocol
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
5-132
82801BA ICH2 and 82801BAM ICH2-M Datasheet