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Example:
Here take ITA-3630 as an example. Assume GPIO 00 is set as Output and GPIO 7 is
set as Input, with two pins interconnected, how to set the corresponding register?
GPIO 00 corresponds to PCA9554 0x40 IO0, while GPIO 07 corresponds to
PCA9554 0x40 IO7.
Set GPIO 00 as Output:
1.
Read SMBUS slave 0x40 register 3 byte value;
2.
Set bit 0 of the value read in step 1 as 0 and write it to SMBUS slave 0x40 regis-
ter 3;
3.
Read SMBUS slave 0x40 register 1 byte value;
4.
Set bit 0 of the value read in step 3 as 0 or 1 according to low or high of the out-
put value, then write it back to SMBUS slave 0x40 register 1.
Set GPIO 07 as Input:
1.
Read SMBUS slave 0x40 register 3 byte value;
2.
Set bit 7 of the value read in step 1 as 1 and write it to SMBUS slave 0x40 regis-
ter 3;
3.
Read SMBUS slave 0x40 register 0 byte value;
4.
Decide low or high of the input value through bit7 value read in step3.
6.3
Function Call for Reference
ICH SMBUS Access Code
(The following code is realized by simulating the access of BIOS to SMBUS. It uses
Borand C++ 3.1 for compiling and is successfully tested under DOS (So far, it is not
tested under other OSs).
#define SMBUS_PORT 0xF040//SMB_BASE?0xF040
typedef unsigned char BYTE;
/////////////////////////////////////////////////////////////////////////////////////////////////////
BYTE
smbus_read_byte(BYTE addr, BYTE offset)
// Read SMBUS Register byte value. Read one byte value each time. addr is slave
address (such as 0x40), and offset is register offset.
{
int
BYTE data;
outportb(SMBUS_PORT + 4, (addr | 1));//
SMB_BASE + 4 (When reading, bit 0 of slave address should be set as 1, so here
addr|1 is available)
newiodelay();//delay
newiodelay();//delay
chk_smbus_ready();// Whether SMBUS is ready
outportb(SMBUS_PORT + 3, offset);// Write register offset to SMB_BASE +
3
ITA-3630 User Manual
i;
Write
slave
54
address
to
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