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IBM Pe!"sonal Co",pute!" MACRO ASlle",ble!"
Version 2.00
1-10
BIOSI
----
06/10/85
INTERRUPT ISH BIOS ROUTINES
06-10-85
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;--
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- - -
-----
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---------
- -- - -
---------------------------------
- - - - -
; GATE A21)
;
-
THIS ROUTINE CONTROLS A SIGNAL WHICH GATES ADDRESS BIT 20.
;
THE GATE A20 SIGNAL
I S AN OUTPUT OF THE 8042 SLAVE PROCESSOR •
ADDRESS BIT 20 SHOULD BE GATED ON BEFORE ENTERING PROTECTED MODE •
IT SHOULD BE GATED OFF AFTER ENTERING REAL MODE FROM PROTECTED
MODE.
INTERRUPTS ARE LEFT DISABLED ON EXIT.
INPUT
IAH) .. DOH
ADDRESS BIT 20 GATE OFF.
IA20 ALWAYS ZERO)
IAH)
=
DFH
ADDRESS BIT 20 GATE ON.
(A20 CONTROLLED BY 802861
OUTPUT
(ALl = OOH
OPERATION SUCCESSFUL.
8042 HAS ACCEPTED COMMAND.
(ALl
=
02H
FAILURE--8042 UNABLE TO ACCEPT COMMAND.
b~~~-~;~--------;~O~-----------------------------------------------------------
-
PUSH
CX
SAVE USERS
(CX)
CLI
DISABLE
INTERRUPTS WHILE USING 8042
CALL
EMPTY 8042
INSURE 8042
INPUT BUFFER EMPTY
JNZ
GATE A20 RETURN
EX I T IF 8042 UNABLE TO ACCEPT COMMAND
MOV
AL.ODlH -
8042 COMMAND TO WRITE OUTPUT PORT
OUT
STATUS PORT .AL
OUTPUT COMMAND TO 8042
CALL
EMPty 8042
WA I T FOR 8042 TO ACCEPT COMMAND
JNZ
GATE A20 RETURN
EX I T
IF 8042 UNABLE TO ACCEPT COMMAND
MOV
AL, AH
-
8042 PORT DATA
g~~L
~~~iY~8~~2
~~T~U~0~0~64~Ai~ ~gc~gi2
PORT DATA
8042 OUTPUT WILL SWITCH WITHIN 20 MICRO SECONDS OF ACCEPTING PORT OATA
GATE A20 RETURN:
-
POP
CX
; RESTORE USERS
(CX)
RET
I - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ---- - - - - - - - - - - - - - - - --
I EMPTY 8042
-THIS ROUTINE WAITS FOR THE 8042
INPUT BUFFER TO EMPTY.
INPUT
NONE
OUTPUT
I
ALl: OOH
8042
I NPUT BUFFER EMPTY
(ZERO FLAG SET)
(AL): 02H
TIME OUT,
8042 INPUT BUFFER FULL
(NON-ZERO FLAG SETI
;
(CX)
- MODIFIED
;
~---
--------
-
--
- - - - - -
---
-
-----
- - - - - - - -
---------------------
- - - - - -- - - - - -
---
-
-
-
EMPTY 80421
-
SUB
CX,CX
(CX) =0, WILL BE USED AS TIME OUT VALUE
EMPTY L:
-
IN
AL.STATUS PORT
READ 8042 STATUS PORT
AND
AL, I NPT BUF FULL
TEST I NPUT BUFFER FUl.L FLAG (BI T
I)
LOOPNZ
EMPTY _L-
-
LOOP UNT I L BUFFER EMPTY OR T I ME OUT
RET
GATE_A20
ENDP
INT 15 H --
( FUNCTION 88 H -
I/O MEMORY SIZE DETERMINE)
---------------
EXT MEMORY
-
THIS ROUTINE RETURNS
THE AMOUNT OF MEMORY
IN THE SYSTEM THAT IS
LOCATED STARTING AT THE l024K ADDRESSING RANGE, AS DETERMINED BY
THE POST ROUT I NES.
NOTE THAT THE SYSTEM MAY NOT BE ABLE TO USE 110 MEMORY UNLESS THERE
I S A FULL COMPLEMENT OF 512K OR 640 BYTES ON THE PLANAR.
TH ISS I ZE
SIZE
I
S STORED I N CMOS AT ADDRESS LOCA
T
IONS 30H AND 3 I H.
AH
=
88H
THE
I/O MEMORY SIZE VARIABLE IS SET DURING POWER ON
OIAGNOSTICS ACCORDING TO THE FOLLOWING ASSUMPTIONS:
I.
ALL
INSTALLED MEMORY
IS FUNCTIONAL.
2.
ALL MEMORY FROM 0 TO 640K MUST BE CONT
I
GUOUS.
OUTPUT
[AX
I
= NUMBER OF CONT I GUDUS
1 K BLOCKS OF MEMORY A
AVAILABLE STARTING AT ADDRESS
1024K.
;
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-
- - - -- - -- - - -- -
---
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----------------
- - - - - - - - - --
EXT_MEMORY
PRDC
MOV
~~O;M~~A~_M-S-LO·H+CMOS-~-~E~-~~E
J H
~~~R~~~EH~~H:7gwM~~6~~
CALL
XCHG
AL,AH
; PUT HIGH BYTE IN POSITION
(AHl
CALL
CMOS READ
;
GET THE LOW BYTE OF
1/0 MEMORY
IRET
-
I RETURN TO USER
EXT_MEMORY
ENDP
5-172
BIOSl
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