C64 ROM: Routine at FD50

FD50: test RAM and find RAM end

Used by the routines at FCE2 and FF87.
FD50	A9 00	LDA #$00	clear A
FD52	A8	TAY	clear index
FD53	99 02 00	STA $0002,Y	clear page 0, don't do $0000 or $0001
FD56	99 00 02	STA $0200,Y	clear page 2
FD59	99 00 03	STA $0300,Y	clear page 3
FD5C	C8	INY	increment index
FD5D	D0 F4	BNE $FD53	loop if more to do
FD5F	A2 3C	LDX #$3C	set cassette buffer pointer low byte
FD61	A0 03	LDY #$03	set cassette buffer pointer high byte
FD63	86 B2	STX $B2	save tape buffer start pointer low byte
FD65	84 B3	STY $B3	save tape buffer start pointer high byte
FD67	A8	TAY	clear Y
FD68	A9 03	LDA #$03	set RAM test pointer high byte
FD6A	85 C2	STA $C2	save RAM test pointer high byte
FD6C	E6 C2	INC $C2	increment RAM test pointer high byte
FD6E	B1 C1	LDA ($C1),Y
FD70	AA	TAX
FD71	A9 55	LDA #$55
FD73	91 C1	STA ($C1),Y
FD75	D1 C1	CMP ($C1),Y
FD77	D0 0F	BNE $FD88
FD79	2A	ROL A
FD7A	91 C1	STA ($C1),Y
FD7C	D1 C1	CMP ($C1),Y
FD7E	D0 08	BNE $FD88
FD80	8A	TXA
FD81	91 C1	STA ($C1),Y
FD83	C8	INY
FD84	D0 E8	BNE $FD6E
FD86	F0 E4	BEQ $FD6C
FD88	98	TYA
FD89	AA	TAX
FD8A	A4 C2	LDY $C2
FD8C	18	CLC
FD8D	20 2D FE	JSR $FE2D	set the top of memory
FD90	A9 08	LDA #$08
FD92	8D 82 02	STA $0282	save the OS start of memory high byte
FD95	A9 04	LDA #$04
FD97	8D 88 02	STA $0288	save the screen memory page
FD9A	60	RTS