;
; Testing RRD instruction
; Also see:
; https://retrocomputing.stackexchange.com/questions/6551/why-does-the-z80-include-the-rld-and-rrd-instructions
;

HL_CONTENT	.DB 	00H

	LD A, 00H
	OUT (00H), A
	OUT (01H), A
	OUT (02H), A
	OUT (03H), A

	; Initialize A and (HL)
	LD A, 10000100B
	LD HL, HL_CONTENT
	LD (HL), 00100000B

	; Display A before operation
	OUT (00H), A

	; Display (HL) before operation
	PUSH AF
	LD A, (HL_CONTENT)
	OUT (01H), A
	POP AF


;
; Performs a 4-bit rightward rotation of the 12-bit number whose 4 most signigifcant bits
; are the 4 least significant
; bits of A, and its 8 least significant bits are in (HL)
;
	RRD		; After execution, expect: A = 10000000, (HL) = 01000010

	; Display A after operation
	OUT (02H), A

	; Display (HL) after operation
	PUSH AF
	LD A, (HL_CONTENT)
	OUT (03H), A
	POP AF

	HALT

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

;
; Routine to add a delay
;
DELAY:
   	PUSH BC

	LD C, 0FFH
DELAY1:	LD B, 0FFH
DELAY2:	NOP
	DJNZ DELAY2
	DEC C
	JR NZ, DELAY1

	POP BC
	RET

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