82801DB Datasheet, PDF (215/587 Pages) Intel Corporation – Intel 82801DB I/O Controller Hub 4 (ICH4)

Functional Description
Process Call
The process call is so named because a command sends data and waits for the slave to return a
value dependent on that data. The protocol is simply a Write Word followed by a Read Word, but
without a second command or stop condition.
When programmed for the Process Call command, the ICH4 transmits the Transmit Slave Address,
Host Command, DATA0 and DATA1 registers. Data received from the device is stored in the
DATA0 and DATA1 registers. The Process Call command with I2C_EN set and the PEC_EN bit
set produces undefined results. Software must force either I2C_EN or PEC_EN to 0 when running
this command. The format of the protocol is shown in Table 5-85 and Table 5-86.
Note: For process call command, the value written into bit 0 of the Transmit Slave Address Register
(SMB I/O register, offset 04h) needs to be 0.
Table 5-85. Process Call Protocol without PEC
Bit
Description
1
Start
2–8
Slave Address - 7 bits
9
Write
10
Acknowledge from Slave
11–18
(Skip This step if I2C_EN bit set)
Command code - 8 bits
19
(Skip This step if I2C_EN bit set)
Acknowledge from slave
20–27
Data byte Low - 8 bits
28
Acknowledge from slave
29–36
Data Byte High - 8 bits
37
Acknowledge from slave
38
Repeated Start
39–45
Slave Address - 7 bits
46
Read
47
Acknowledge from slave
48–55
Data Byte Low from slave - 8 bits
56
Acknowledge
57–64
Data Byte High from slave - 8 bits
65
NOT acknowledge
66
Stop
Intel^® 82801DB ICH4 Datasheet
215