Functional Description
5-122
Intel
82801BA ICH2 Datasheet
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 5-80
.
Table 5-79. Write Byte/Word Protocol
Write Byte Protocol
Write Word Protocol
Bit
Description
Bit
Description
1
Start
1
Start
2:8
Slave Address - 7 bits
2:8
Slave Address - 7 bits
9
Write
9
Write
10
Acknowledge from slave
10
Acknowledge from slave
11:18
Command code - 8 bits
11:18
Command code - 8 bits
19
Acknowledge from slave
19
Acknowledge from slave
20:27
Data Byte - 8 bits
20:27
Data Byte Low - 8 bits
28
Acknowledge from Slave
28
Acknowledge from Slave
29
Stop
29:36
Data Byte High - 8 bits
37
Acknowledge from slave
38
Stop
Table 5-80. Read Byte/Word Protocol
Read Byte Protocol
Read Word Protocol
Bit
Description
Bit
Description
1
Start
1
Start
2:8
Slave Address - 7 bits
2:8
Slave Address - 7 bits
9
Write
9
Write
10
Acknowledge from slave
10
Acknowledge from slave
11:18
Command code - 8 bits
11:18
Command code - 8 bits
19
Acknowledge from slave
19
Acknowledge from slave
20
Repeated Start
20
Repeated Start
21:27
Slave Address - 7 bits
21:27
Slave Address - 7 bits
28
Read
28
Read
29
Acknowledge from slave
29
Acknowledge from slave
30:37
Data from slave - 8 bits
30:37
Data Byte Low from slave - 8 bits
38
NOT acknowledge
38
Acknowledge
39
Stop
39:46
Data Byte High from slave - 8 bits
47
NOT acknowledge
48
Stop
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