Some Z80 ASM for CP/M

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+*.hex

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+; tiktok.asm
+; ASM dialect is for crasm/z80, producing Intel HEX.
+; Compile using "crasm -o tiktok.hex tiktok.asm" and transfer
+; to CP/M system for final conversion to COM file using LOAD.COM
+;
+; A sample program that uses a busy-waiting spinloop
+; to produce 1ms delays. 5*200 iterations of calls to
+; the delay loop is made, to provide a 1sec delay per "Tick".
+; 60 iterations of printint "Tick" to the console is done
+; for a full minute of waiting time.
+; Console output is done using CP/M BDOS call 9 (C_WRITRSTR)
+
+CPU Z80
+OUTPUT HEX
+
+; CP/M constants used
+STROUT EQU 9
+BDOS   EQU 5
+
+; Start COM file at TPA start (Origin 0x100)
+* = $100
+START          LD DE, STARTMSG
+               LD C, STROUT
+               CALL BDOS
+
+               LD A, 60
+LOOP           PUSH AF
+
+               LD DE, MESSAGE
+               LD C, STROUT
+               CALL BDOS
+
+               LD B, 5 ; 5 * 200 msec = 1000ms = 1 sec :P
+SEC            LD A, 200
+               CALL DELAY
+               DEC B
+               JR NZ, SEC
+
+               POP AF
+               DEC A
+               JR NZ, LOOP
+
+               LD DE, STOPMSG
+               LD C, STROUT
+               CALL BDOS
+
+               RET
+
+; Delay routine, A register contains number of Delay iterations.
+; Does not clobber, but A is reduced to zero on completion
+; Values tried (may be good) for 7.3728MHz: C=13, B=44
+DELAY           PUSH BC                        ; Save B and C registers
+DLY_START       LD C, 13               ; Coarse factor
+DLY_LOOPO       LD B, 44               ; Fine factor
+DLY_LOOPI       DJNZ DLY_LOOPI         ; Decrement B until BZero
+                DEC C                  ; Decrement C ..
+                JR NZ, DLY_LOOPO       ; .. until zero
+                DEC A                  ; Do next main iteration
+                JR NZ, DLY_START       ; until given numer is zero
+                POP BC                 ; Restore B and C registers
+                RET                    ; Return from delay.
+
+; String constants here, to avoid having them clobber $100H
+; Note CP/M BDOS call 9 format, $ is string terminator.
+STARTMSG ASC "Timertest\r\n$"
+MESSAGE ASC "Tick\r\n$"
+STOPMSG ASC "Done\r\n$"