Intel
82801BA ICH2 Datasheet
5-125
Functional Description
l
I
2
C Read
This command allows the ICH2 to perform block reads to certain I
2
C devices (e.g., serial
E
2
PROMs). The SMBus Block Read sends both the 7-bit address, as well as the Command field.
This command field could be used as the extended 10-bit address for accessing I
2
C devices that use
10-bit addressing.
However, this does not allow access to devices using the I
2
C “Combined Format” that has data
bytes after the address. Typically, these data bytes correspond to an offset (address) within the
serial memory chips.
Note:
This new command is supported independent of the setting of the I
2
C_EN bit.
For I
2
C Read command, the value written into bit 0 of the Transmit Slave Address Register (SMB
I/O register, offset 04h) needs to be 0. The format that is used for the new command is shown in
Table 5-83
:
Table 5-82. Block Read/Write Protocol
Block Write Protocol
Block Read 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
Byte Count - 8 bits
(Skip this step if I
2
C_En bit set)
20
Repeated Start
28
Acknowledge from Slave
(Skip this step if I2C_EN bit set)
21:27
Slave Address - 7 bits
29:36
Data Byte 1 - 8 bits
28
Read
37
Acknowledge from Slave
29
Acknowledge from slave
38:45
Data Byte 2–8 bits
30:37
Byte Count from slave - 8 bits
46
Acknowledge from slave
38
Acknowledge
...
Data Bytes / Slave
Acknowledges...
39:46
Data Byte 1 from slave - 8 bits
...
Data Byte N - 8 bits
47
Acknowledge
...
Acknowledge from Slave
48:55
Data Byte 2 from slave - 8 bits
...
Stop
56
Acknowledge
...
Data Bytes from slave/Acknowledge
...
Data Byte N from slave - 8 bits
...
NOT Acknowledge
...
Stop
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