From: Jon Langseth <jon.langseth@ntnu.no>
Date: Mon, 23 Jan 2017 17:49:13 +0000 (+0100)
Subject: Some Z80 ASM for CP/M
X-Git-Url: https://git.defcon.no/?a=commitdiff_plain;h=4ac76fc65056e1aaa0e1a5a83284d1fc63da733d;p=z80cpm

Some Z80 ASM for CP/M
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4ac76fc65056e1aaa0e1a5a83284d1fc63da733d
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+*.hex
diff --git a/tiktok.asm b/tiktok.asm
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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$"