Lately I’ve been working on reading the CF card contents on the PowerPak. I thought I’d share my findings so far.

This post is just to publish a few of my notes on reading the CF card contents on the PowerPak on the NES.

The information was gained from disassembling and reverse-engineering the PowerPak boot ROM, thus it’s incomplete. At this point, I’m only able to read sectors; Not write.

The PowerPak boot ROM used was obtained from the PowerPak Mappers v1.34 archive found on RetroZone‘s site.

;---------------------------------------------------------------- 
; Notes
;---------------------------------------------------------------- 
;
; Reading from $5007 will return the status of the CF card
; 	0xFF - No card inserted
; 	0x80 - Card busy[1]
; 	0x58 - Card busy[1]
; 	0x50 - Unknown
; 	0x01 - Fatal card read error
;
; Reading form $5001 - Unknown
;
; Reading from $5000 - Read bytes from sector
;
; Writing to $5402
;   0x01 - Enter CF access mode. PRG ROM will be disabled[2] during this time.
;   0x00 - Leave CF access mode. PRG ROM is now available as usual.
;
; Writing to $5407
;   0x20 - Unknown
;
; Writing to $5403 - $5405
;   Sector address
;
; Writing to $5406
;   Unknown[3]
;
; [1] - I'm not sure what the different "busy" codes means, but the bottom line is that
;       the card is not ready to be read from just yet.
;
; [2] - What might actually happen here is that the boot ROM will be accessable, 
;       but I haven't tested this yet. All I know is that the PRG ROM will be inaccessable.
;
; [3] - It would be logical that this is the 4th byte of the sector address, but
;       I can successfully load the first sectors of the card when writing $E0 here.
;       Dunno what it REALLY is... I'll have to experiment with this later.

LoadCFCardSector:

	; Enter CF access mode.
	; At this point, the PRG ROM will be disabled
	LDA #$01
	STA $4207
	
	JSR WaitForCard
	
	LDA #$01
	STA $5402
	
	; Sector to read
	LDA SectorAddr0
	STA $5403
	
	LDA SectorAddr1
	STA $5404
	
	LDA SectorAddr2
	STA $5405
	
	LDA #$E0	
	STA $5406
	
	LDA #$20
	STA $5407
	NOP
	NOP
		
	JSR WaitForCard2

	; Load the 512 bytes of the sector into memory
	LDX #$00
	LoadLoop:
		LDA $5000
		STA $0500,X
		INX
		BNE LoadLoop
	
	LDX #$00
	LoadLoop:
		LDA $5000
		STA $0600,X
		INX
		BNE LoadLoop
	
	; Leave CF access mode.
	; PRG ROM is now accessable again, and no further CF reads can be made
	; until CF access mode is entered again.
	LDA #$00
	STA $4207
		
	RTS

WaitForCard:
	LDA $5007
	AND #$80
	BNE WaitForCard
	RTS
	
WaitForCard2:
	LDA $5007
	AND #$58
	CMP #$58
	BNE WaitForCard2
	RTS
	
CheckError:
	LDA $5007
	AND #$01
	CMP #$01
	BEQ CheckError_Found
	RTS
	CheckError_Found:
	
	; There was an error.
	; Do something here...
	
	RTS