Watchdog Timer Configuration - American Megatrends PMB-901LF User Manual

Appendix B Technical Summary

WATCHDOG TIMER CONFIGURATION

The I/O port address of the watchdog timer is 2E (hex) and 2F (hex). 2E (hex) is the
address port. 2F (hex) is the data port. User must first assign the address of register by
writing address value into address port 2E (hex), then write/read data to/from the
assigned register through data port 2F (hex).
Configuration Sequence
To program W83627UHG configuration registers, the following configuration
sequence must be followed:
(1) Enter the extended function mode
(2) Configure the configuration registers
(3) Exit the extended function mode
(1) Enter the extended function mode
To place the chip into the Extended Function Mode, two successive writes of 0x87
must be applied to Extended Function Enable Registers (EFERs, i.e. 2Eh or 4Eh).
(2) Configure the configuration registers
The chip selects the Logical Device and activates the desired Logical Devices through
Extended Function Index Register (EFIR) and Extended Function Data Register
(EFDR). The EFIR is located at the same address as the EFER, and the EFDR is
located at address (EFIR+1). First, write the Logical Device Number (i.e. 0x07) to the
EFIR and then write the number of the desired Logical Device to the EFDR. If
accessing the Chip (Global) Control Registers, this step is not required. Secondly,
write the address of the desired configuration register within the Logical Device to the
EFIR and then write (or read) the desired configuration register through the EFDR.
(3) Exit the extended function mode
To exit the Extended Function Mode, writing 0xAA to the EFER is required. Once the
chip exits the Extended Function Mode, it is in the normal running mode and is ready
to enter the configuration mode.
Page: B-15
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PMB-901LF USER S MANUAL