8SA1Sim/examples/printstring.asm

;	printstring.asm
;	
;	This is a simple demonstration routine for the emulator to take a null terminated string from RAM
;	and display it out to the emulators text printer.
;	The routine takes a simple argument on the stack with the address of the string.
;	The routine will use the DISPLAY variable set in .data 
;
;	Version: 0.2.1

		GLOBAL	START
		GLOBAL 	PRINTSTRING
	
		SECTION .text
START:			LDAB	MYSTRING				; Put string address into AB
				PHAB							; and push to the stack
				JSR	PRINTSTRING				    ; Call PRINTSTRING routine

		SECTION .printstring
PRINTSTRING:	PLAB							
				PHAB							; Get the address of the string
				LDA 	$DISPLAY				; Set the output address
				PHA
				LDAB 	$DISPLAY+1				; Set the output address
				PHAB
PRINTLOOP:		LDAB	CD
				CMP		A,B
				BEQ		RETURN					; If we pull a 0, or null then we are done
				STAL	[SP]
				ADD		C,$1					; Increment our string location by 1
				BCS		ROLLOVER				; If it rolls over we need to go handle high byte
				PLAB
				ADD		A,$1					; Icrement our output by 1
				PHAB
				JMP		PRINTLOOP				; Loop back and keep reading in the string
ROLLOVER:		ADD		D, $1
				PLAB
				ADD		B, $1
				PHAB
				JMP		PRINTLOOP				; Loop back and keep reading in the string
RETURN:			PLAB							; To return we need to clean up our stack use first
                PLA
				RTS
				
		SECTION	.data
DISPLAY			equ		D00000h
MYSTRING		DB		"Welcome to the MatCat 8SA1 Computer Simulator!\n\nThis is a full hardware simulation of the computer to allow for easy development testing.  It is currently a heavy work in progress as it is very early alpha, so check back often for new features!\n\n\nThis demo  can be seen in the examples folder on the git page at: \nhttps://mygit.space/MatCat.OpenSource/8SA1Sim", 0