Classic Computer Magazine Archive COMPUTE II ISSUE 1 / APRIL/MAY 1980 / PAGE 46

24 Hour Clock for SYM-1 BASIC

A. M. Mackay
600 Sixth Avenue West,
Owen Sound, Ontario, Canada
N4K 5E7

Load this program in your SYM-1 and enter G 0FB8. It will start a clock, display the memory you should enter to protect the program, then automatically transfer you to BASIC. Be sure to enter the amount of memory shown on the CRT. If you don't, you will lose the program.

The clock sits at the very top of your memory, and will not interfere with your BASIC – in fact, you won't even know it's there unless you call it. But it will be there when you want it for control operations, time delays for games, or whatever. You can even use your CRT as a time-of-day clock. It will keep ticking away until you hit “reset” or turn your SYM off.

As written, it is a 24 hour clock. If you want a 12 hour clock, change the contents of location 0FAD to “C0”.

This clock uses timer 1 of U29 to interrupt the program every 50 ms. “COUNT” totals these interrupts, and after each 20 interrupts one is added to “SECS”. Timer 2 and the input ports of U29 are not affected, and can be used for other purposes.

The program is written for a SYM-1 with 4K memory. It can be relocated upwards by changing all the “0F” bytes to “1F” or whatever. Also, change the bytes in locations 0FF9 to 0FFC. For example, for 8K, change these bytes to 37 35 34 38. The formula is 131 less than the number of free bytes usually displayed after going to BASIC, with a “3” before each digit.

The program as written keeps the time, starting at 0h, 0m, 0s from the time you enter G 0FB8. If you prefer time of day, enter the following (for 4K):

POKE &"0F7D", hour (in 24 hour time), CR
POKE &"0F7E", minute, CR
POKE &"0F7F", second, then hit CR on the exact second.

To use the clock in a BASIC program, enter the following BASIC command:

10 H = PEEK(&"0F7D"):M = PEEK(&"0F7E"):S = PEEK(&"0F7F")

Then use the variables H, M and S as you require them. To use your CRT as a clock, use the following program:

10 - as in the paragraph above.
20 PRINT CHR$(12)
30 PRINT H;":";M;":";S
40 FOR X = 1 TO 785: NEXT
50 GOTO 10
60 END

If you can turn cursor off, the clock will look much better.

The actual clock program ends at 0FDE. The rest of the program puts out the memory requirements on the CRT. If you don't want to transfer to BASIC, or if you don't have a CRT, put 4C 00 80 in locations 0FDF - 0FE1. You can then access the time by going to M 0F7D (hour), 0F7E (mins) and 0F7F (secs).

If anyone wants it, perhaps I'll write a routine for a future issue that will display the time on the SYM-1 LED readouts.

                0010            .BA $0F7C    ;THIS PROGRAM STARTS A
                0020 ACCESS     .DE $8B86    ;24 HOUR CLOCK AND
                0030 OUTVEC     .DE $A663    ;DISPLAYS THE AMOUNT OF
                0040 IRQVEC     .DE $A67E    ;REMAINING MEMORY TO BE
                0050 CLRINT     .DE $AC04    ;ENTERED WHEN REQUESTED
                0060 T1CH       .DE $AC05    ;THEN AUTOMATICALLY
                0070 T1LL       .DE $AC06    ;TRANFERS TO BASIC.
                0080 ACR        .DE $AC0B    ;TIME IS NOT DISPLAYED UNTIL
                0090 IFR        .DE $AC0D    ;REQUESTED BY BASIC PROGRAM.
                0100 IER        .DE $AC0E  
                0110 BASIC      .DE $C000  
0F7C- 14        0120 COUNT      .BY $14      ;SET COUNT TO 20
0F7D- 00        0130 HOUR       .BY $00      ;START TIME AT 00 HOURS
0F7E- 00        0140 MINS       .BY $00      ;              00 MINUTES
0F7F- 00        0150 SECS       .BY $00      ;              00 SECONDS
                0170 ;***INTERRUPT ROUTINE*** 
0F80- 48        0190 CLOCK      PHA 
0F81- CE 7C 0F  0200            DEC COUNT    ;SEE IF 1 SEC HAS PASSED
0F84- D0 2D     0210            BNE EXIT     ;IF NO, EXIT
0F86- A9 14     0220            LDA #20      ;IF YES, -
0F88- 8D 7C 0F  0230            STA COUNT    ; RESTORE COUNT AND
0F8B- EE 7F 0F  0240            INC SECS     ; ADD 1 TO SECS.
0F8E- AD 7F 0F  0250            LDA SECS     ;SEE IF 60 SECS HAS PASSED
0F91- 38        0260            SEC 
0F92- E9 3C     0270            SBC #60 
0F94- D0 1D     0280            BNE EXIT     ;IF NO, EXIT
0F96- 8D 7F 0F  0290            STA SECS     ;IF YES RESET SECS TO 0 AND
0F99- EE 7E 0F  0300            INC MINS     ;ADD 1 TO MINS
0F9C- AD 7E 0F  0310            LDA MINS     ;SEE IF 60 MINS HAS PASSED
0F9F- E9 3C     0320            SBC #60 
0FA1- D0 10     0330            BNE EXIT     ;IF NO, EXIT
0FA3- 8D 7E 0F  0340            STA MINS     ;IF YES RESET MINS TO 0 AND
0FA6- EE 7D 0F  0350            INC HOUR     ;ADD 1 TO HOUR
0FA9- AD 7D 0F  0360            LDA HOUR     ;SEE IF 24 HOURS HAS PASSED
0FAC- E9 18     0370            SBC #24      ;IF NO,
0FAE- D0 03     0380            BNE EXIT     ; EXIT
0FB0- 8D 7D 0F  0390            STA HOUR     ;IF YES, RESET HOUR TO 0
0FB6- 68        0410            PLA 
0FB7- 40        0420            RTI 
                0440 ;***INITIATE TIMER*** 
0FBB- A9 80     0470            LDA #$80     ;SET IRQ
0FBD- 8D 7E A6  0480            STA IRQVEC   ;  VECTOR
0FC0- A9 0F     0490            LDA #$0F     ;   TO
0FC2- 8D 7F A6  0500            STA IRQVEC+$1        ; "CLOCK"
0FC5- A9 C0     0510            LDA #$C0     ;SET BITS 6 AND 7
0FC7- 8D 0B AC  0520            STA ACR      ;FOR FREE-RUNNING MODE
0FCA- 8D 0E AC  0530            STA IER      ;AND T1 INTERRUPT ENABLE
0FCD- AD 0D AC  0540            LDA IFR      ;CLEAR T1 FLAG BIT 6 BUT
0FD0- 29 BF     0550            AND #$BF     ;DON'T DISTURB OTHER
0FD2- 8D 0D AC  0560            STA IFR      ;IFR BITS
0FD5- A9 50     0570            LDA #$50     ;SET
0FD7- 8D 06 AC  0580            STA T1LL     ; TIMER
0FDA- A9 C3     0590            LDA #$C3     ;  FOR 1/20 SEC AND
0FDC- 8D 05 AC  0600            STA T1CH     ;   START TIMER
                0620 ;***BASIC MEMORY OUT*** 
0FDF- A2 00     0640 DISPMEM    LDX #$00     ;START OF
0FE4- 20 63 A6  0660            JSR OUTVEC   ; 
0FE7- E8        0670            INX          ; TO
0FE8- C9 04     0680            CMP #$04     ; 
0FEA- F0 03     0690            BEQ GOBAS    ; DISPLAY
0FEC- 4C E1 0F  0700            JMP OUTMEM   ; REMAINING
0FEF- 4C 00 C0  0710 GOBAS      JMP BASIC    ; MEMORY
0FF2- 0D 0A 4D  0720 TABLE      .BY $0D $0A 'MEM. 3965' $0D $0A $04
0FF5- 45 4D 2E 
0FF8- 20 33 39 
0FFB- 36 35 0D 
0FFE- 0A 04 
                0730            .EN          ;END OF PROGRAM