.ORG 100h			; CP/M programs start address

		JP START			; Go to program start
	
;
; Variable storage space
;

Stack1		.DW 	0			; Place to save old stack
Sbot		.DS 	64			; Temp stack for us to use

	;
	; Constants
	;

STOP		.EQU $-1			; Top of our stack
BDOS		.EQU 5				; Address of BDOS entry
LEDS		.EQU 00H			; Digital I/O board			

	;
	; Start of code segment
	;

START: 
		LD HL, 0000H			; HL = 0
		ADD HL, SP			; HL = SP
		LD (Stack1), HL			; Save original stack
		LD HL, STOP			; HL = address of new stack
		LD SP, HL			; Stack pointer = our stack
	
		LD B, 0FH
REPEAT:
		LD A, 01010101B
		OUT (LEDS), A			; Send the pattern to the port
    		CALL DELAY			; A little delay
		CALL DELAY

    		LD A, 10101010B
    		OUT (LEDS), A			; Send the pattern to the port
		CALL DELAY			; A little delay
		CALL DELAY

		DJNZ REPEAT

		; ------------------------------------------------------------
		; Finish and return to CP/M
EXIT: 
		LD HL, (Stack1)			; HL = entry stack address
		LD SP, HL			; SP = value on entry
		RET				; Return control back to CP/M

;--------------------------------------------------------------------------------------

	;
DELAY:  ; Routine to add a delay 
	;
        	PUSH BC
		
		LD C, 0FFH
DELAY1:        	LD B, 0FFH
DELAY2:		NOP
       		DJNZ DELAY2
        	DEC C
        	JR NZ, DELAY1
        
		POP BC
        	RET
		
;--------------------------------------------------------------------------------------
.END