====== Detect Retro Replay hardware ======

By FMan.

This is a straight-forward detection routine to find out if a Retro Replay is active on the system. It works by writing different bytes to the same address in the $8000-$9FFF range. If there is no cart, all of the writes will go to normal RAM and the latest byte will be the one read back. Otherwise some of them go to different RR RAM banks. Successful readback of both bytes written to the RR RAM will be taken to signal the presence of a Retro Replay.

Find the print routine [[base:string manipulation routines|elsewhere]]. This routine is well tested and is believed to reliably identify either the presence or nonexistence of an RR.

<code>
; Retro Replay detection using RR RAM writes by FMan/Tropyx

	!to "rrdetect.prg",cbm

; note that this code puts the computer in Ultimax mode
; a few times, so it must be located below $1000 in RAM

	*=$c00

RRDetect

	sei
	lda #66
	sta $de01	; configure the cart
	ldx #$a4
	ldy #$6a
	lda #$2b	; select RAM bank 1 and
	sta $de00	; invoke Ultimax mode to
	sty $8080	; write into the RR RAM
	lda #$23
	sta $de00
	sta $8080	; write to normal RAM now
	lda #$3b
	sta $de00	; select RAM bank 3 and
	stx $8080	; write another byte there
	lda #$28
	sta $de00
	cli
	cpy $8080	; see if the original byte survived
	bne NoRR	; subsequent writes to same address
	lda #$38
	sta $de00	; do another check with the second
	cpx $8080	; byte that was written to bank 3
	beq RRFound
NoRR	lda #<NoRRstr
	sta dst
	lda #>NoRRstr
	sta dst+1
	jsr print	; see note above
	rts

RRFound	nop		; continue your program using the Retro Replay
	rts

NoRRstr	!pet 13,"no retro replay was found.",13,0
</code>