IBM PC CONVERTIBLE

Timer 0 Interrupt S (TMRO_INTS)
; *********************************************************************
TMRO_INT8
DESCRIPTION:
THIS ROUTINE HANDLES THE TIMER INTERRUPT FROM
CHANNEL 0 OF THE 8253 TIMER. INPUT FREQUENCY
IS 1.19318 MHZ AND THE DIVISOR IS 65536, RESULTING
IN APPROX. 18.2 INTERRUPTS EVERY SECOND.
THE INTERRUPT HANDLER MAINTAINS A COUNT OF INTERRUPTS
SINCE POWER ON TIME, WHICH MAY BE USED TO ESTABLISH
TIME OF DAY.
THE INTERRUPT HANDLER ALSO DECREMENTS THE MOTOR
CONTROL COUNT OF THE DISKETTE, AND WHEN IT EXPIRES,
WILL TURN OFF THE DISKETTE MOTOR, AND RESET THE
MOTOR RUNNING FLAGS.
THE INTERRUPT HANDLER WILL ALSO INVOKE A USER ROUTINE
THROUGH INTERRUPT lCH AT EVERY TIME TICK. THE USER
MUST CODE A ROUTINE AND PLACE THE CORRECT ADDRESS IN
THE VECTOR TABLE.
INPUT: OS = DATA
OUTPUT: AX=O (GOOD RETURN)
AH=40 (NON_FATAL ERROR) AL=63 (RTC ERROR)
RESTRICTIONS: NONE
REGISTERS MODIFIED: NONE
INTERRUPTS: FORCED ON (STI)
I NTERNALL Y REFERENCED ROUTI NES: NONE
; EXTERNALLY REFERENCED ROUTI NES: DDS, INT lCH, I NT 4AH
; **********************************************************************
0330 TMRO_INT8
PROC
FAR
0330 FB
STI
I NTERRUPTS BACK ON
033E IE PUSH
OS
033F 50 PUSH
AX
0340 52 PUSH
OX
SAVE MACHINE STATE
0341 E8 0000 E
CALL DDS
0344 FE OE 007B R DEC EVENLTIM_OUT DEC WAIT ON EVNT TIMEOUT CTR
0348 FF 06 006C R INC TIMER_LOW INCREMENT TIME
034C 75 04 JNZ
T4
TESLDAY
034E FF 06 006E INC
TlMEILHIGH
INCREMENT HIGH WORD OF TIME
CHECK TIMER FOR 24 HOUR ROLL OVER
0352
0352
0357
0359
035F
83 3E 006E R 18
75 15
81 3E 006C R OOBO
75 00
0361 2B CO
0363 A3 006E R
0366 A3 006C R
0369 C6 06 0070 R 01
T4:
CMP
JNZ
CMP
JNZ
; TESLDAY
TIMER_HIGH,COUNTS_DALHI
; TST FOR CNT
T5 ; DISKETTE_CTL
TIMER_LOW, COUNTS_DAY _LO
T5 ; DISKETTE_CTL
TIMER HAS GONE 24 HOURS
SUB
MOV
MOV
MOV
AX,AX
TlMER_HIGH,AX
TIMER_LOW,AX
TIMEILOFL,1
TEST FOR DISKETTE TIME OUT
036E T5:
DISKETTE_CTL
24 HOURS
036E 80 3E 0040 R 00 CMP SKI P MOTOR OFF I F ALREADY 0
2-166 ROM BIOS