PROGRAM LISTING: 85-09/TIMER2.ASM

0100 ;TIMER 2
0110 ;BY FRED PINHO
0120 ;(c) 1985, ANTIC PUBLISHING
0160     *=  $0600   ;RELOCATABLE
0170 ;SINCE MAC/65 USES PAGE 6, ASSEMBLE TO DISK. RECOVER FILE WITH DOS.
0180 ;FOR DEBUGGING, ASSEMBLE WITH AN OFFSET VIA THE .SET AND .OPT DIRECTIVES.
0190     .TITLE "LISTING 2"
0200     .TAB 14,18,26
0210     .SET 1,4
0220 SETVBV = $E45C
0230 XITVBV = $E462
0240     CLD         ;MUST BE DONE
0250     LDA 1021    ;TIMER ACTIVATED?
0260     BNE GOON    ;YES. SKIP AROUND
0270     LDA #1      ;NO. SET DELAY FOR IMMEDIATE DISPLAY
0280     STA 1028
0290     LDA #255    ;SET TO INDICATE ACTIVE TIMER
0300     STA 1021
0310     STA 558     ;SET TIMER FLAG
0320     LDY 1025    ;DESIRED TIME,LOW
0330     LDX 1026    ;HIGH
0340     LDA #5      ;TIMER 5 TO BE ENABLED
0350     JSR SETVBV  ;DOES THE JOB
0360 GOON DEC 1028   ;CALCULATE TIME?
0370     BNE EXIT    ;NOT YET. BYPASS ROUTINE
0380     LDA #10     ;YES. RESET DELAY COUNTER
0390     STA 1028
0400     LDA 544     ;GET TIMER LO BYTE
0410     STA 1022
0420     LDA 545     ;HI BYTE
0430 DIVIDE LDX #8   ;DIVIDE BY 60
0440 LOOP1 ASL 1022  ;TO GET TOTAL SECONDS
0450     ROL A
0460     CMP #60
0470     BCC BRCH1
0480     SBC #60
0490     INC 1022
0500 BRCH1 DEX 
0510     BNE LOOP1
0520     STA 1023
0530 ;TOTAL SECONDS STORED IN REGISTER 1022
0540     LDX #8      ;DIVIDE BY 60
0550     LDA #0      ;TO GET MINUTES
0560 LOOP2 ASL 1022
0570     ROL A
0580     CMP #60
0590     BCC BRCH2
0600     SBC #60
0610     INC 1022
0620 BRCH2 DEX 
0630     BNE LOOP2
0640     STA 1023
0650 ;MINUTES IN 1022,REMAINING SECONDS IN 1023
0660 ;NOW DIVIDE BY 10 TO GET HI AND LO DIGITS OF DECIMAL NUMBER
0670     LDX #8
0680     LDA #0
0690 LOOP3 ASL 1023
0700     ROL A
0710     CMP #10
0720     BCC BRCH3
0730     SBC #10
0740     INC 1023
0750 BRCH3 DEX 
0760     BNE LOOP3
0770     STA 1024
0780 ;SECONDS(TENS PLACE) IN 1023
0790 ;SECONDS(UNIT PLACE) IN 1024
0800 DISPLAY CLC     ;STORE 3 DIGITS INTO DISPLAY AREA
0810     LDY #0
0820     LDA 1022    ;MINUTES
0830     ADC #16     ;CONVERT TO SCREEN CODE
0840     STA (208),Y ;STORE
0850     INY 
0860     LDA #26     ;SCREEN CODE FOR ':'
0870     STA (208),Y
0880     INY 
0890     LDA 1023    ;SECONDS(HI)
0900     ADC #16
0910     STA (208),Y
0920     INY 
0930     LDA 1024    ;SECONDS(LO)
0940     ADC #16
0950     STA (208),Y
0960     LDA 558     ;TIMER DONE?
0970     BEQ DISABLE ;YES
0980 EXIT JMP XITVBV ;NO. JUST RETURN TO VBI
0990 DISABLE LDA #$62 ;RESTORE ORIGINAL VBI VECTOR
1000     STA 548
1010     LDA #$E4
1020     STA 549
1030     JMP XITVBV  ;EXIT
1040     .END