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Revision 1.1

Core Logic Module (Continued)

5.2.7

I/O Ports 092h and 061h System Control

The Core Logic module supports control functions of I/O

Ports 092h (Port A) and 061h (Port B) for PS/2 compatibil-

ity. I/O Port 092h allows a fast assertion of the A20M# or

CPU_RST. (CPU_RST is an internal signal that resets the

CPU. It is asserted for 100 µs after the negation of POR#.)

I/O Port 061h controls NMI generation and reports system

status.The Core Logic module generates an SMI for every

internal change of the A20M# state and the SMI handler

sets the A20M# state inside the GX1 module. This method

is used for both the Port 092h (PS/2) and Port 061h (key-

board) methods of controlling A20M#.

5.2.7.1

I/O Port 092h System Control

I/O Port 092h allows for a fast keyboard assertion of an

A20# SMI and a fast keyboard CPU reset. Decoding for this

The assertion of a fast keyboard A20# SMI is controlled by

either I/O Port 092h or by monitoring for the keyboard com-

mand sequence (see Section 5.2.8.1 "Fast Keyboard Gate

Address 20 and CPU Reset" on page 133). If bit 1 of I/O

Port 092h is cleared, the Core Logic module internally

asserts an

A20M#, which in turn causes an SMI to the

GX1 module. If bit 1 is set, A20M# is internally deasserted,

again causing an SMI.

The assertion of a fast keyboard reset (WM_RST SMI) is

controlled by bit 0 in I/O Port 092h or by monitoring for the

keyboard command sequence (write data = FEh to I/O port

64h). If bit 0 is changed from 0 to 1, the Core Logic module

generates a reset to the GX1 module by generating a

WM_RST SMI. When the WM_RST SMI occurs, the BIOS

jumps to the Warm Reset vector. Note that Warm Reset is

not a pin, it is under SMI control.

5.2.7.2

I/O Port 061h System Control

Through I/O Port 061h, the speaker output can be enabled,

the status of IOCHK and SERR can be read, and the state

of the speaker data (Timer2 output) and refresh toggle

(Timer1 output) can be read back.

5.2.7.3

SMI Generation for NMI

Figure 5-10 shows how the Core Logic module can gener-

ate an SMI for an NMI. Note that NMI is not a pin.

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