F84045 Asiliant Technologies, F84045 Datasheet - Page 78

• Manufacturer Part Number: F84045
• Manufacturer: Asiliant Technologies

Specifications of F84045

• Lead Free Status / Rohs Status: Not Compliant

5.3.2. Emulated 8042 KBRESET# and GATEA20
The CPU reset and GATEA20 functions are normally done by the external 8042 or internal KBC. The CPU issues I/O
commands to the 8042 to manipulate these signals. The 4041 chip may be configured to monitor these signals and
simulate the RESET and GATEA20 functions of the 8042. Optionally, the commands may be blocked to the 8042 in
order to speed up the operation.
The commands are written to the 8042 through address 64h. The commands which affect GateA20 and KBRESET#
are:
To take GATEA20 high a program could use either the D1 or Fx codes. (Pulsing GATEA20 will pulse it low, then
high, leaving it high). To take GATEA20 low, Write Output Port must be used. The self test must be decoded simply
because it does effect the pin. Programs do not use this as a method of changing it.
A CPU Reset requires the Fx command. Using the D1 command to do it will keep CPU reset low forever, recoverable
only by hardware reset.
The Fx and D1 commands are optionally blocked from the 8042. The 4041 does this by not issuing an IOW# for them.
F0, F1, F2, F4, F5, F6, F8, F9, FA, FC, FD, and FE commands are blocked. The D1 commands are a bit more
complicated and follow these rules:
This will block all three writes in the typical sequence, which is as follows:
The GATEA20 and KBRESET# pins of the 8042 may remain connected to the 4041 chip's GATEA20 input pin when
the GATEA20 and KBRESET# functions are being emulated. They will continue to be ORed with the emulated
versions.
Revision 1.0
AA
D1
Fx
Write the D1 command to port 64.
Write the data to port 60.
Write an FF command to the keyboard controller to detect when it has finished updating GATEA20.
Self Test. KBRESET# and GATEA20 go high.
Write Output Port. Next byte written to port 60 is the data. Bit 0=KBRESET#, bit 1=GATEA20.
Pulse output ports.
F0, F1, F4, F5, F8, F9, FC, and FD take GATEA20 high.
All of the even ones cause a KBRESET#
D1 commands are blocked.
Following a D1 command, the next write to port 60 is blocked. If another (non D1) command occurs
before port 60 is written, the next port 60 write is not blocked.
2/10/95
Following a blocked port 60 write, if an FF command (writing FF to port 64) occurs as the
next write to the keyboard controller, it is blocked also. If multiple FF commands are issued
only the first one is blocked.
Subject to change without notice
77
Preliminary
Functional Description
CS4041