Advanced/RH Technical Product Specification •• Page 46
Appendix K −− Soft-off Control
The Advanced/RH design supports Soft-off control via the SMM code in the BIOS. The CS1 pin out of the National
306B Ultra I/O controller is connected to the Soft-off control line in our power supply circuit.
The registers in the Ultra I/O controller that sets the I/O address and control of the CS1 pin is NOT setup until the
SMM code is activated. The code performs the following operations:
OUT 0Ch to I/O port 2Eh
OUT 75h to I/O port 2Fh
OUT 11h to I/O port 2Eh
OUT 00h to I/O port 2Fh
OUT 0Dh to I/O port 2Eh
OUT A0h to I/O port 2Fh
After setting the above registers, any read operation to I/O location 75H will trigger the Soft-off circuit and turn the
power supply off.
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