PAGE
	SBTTL "DISK ACCESS: ACORN"

	;****************************
	;READ/WRITE A BLOCK TO IOBUFF
	;****************************

	;ENTRY:	TRACK SET TO TRACK # (0-79)
	; 	SECTOR SET TO SECTOR # (0-7)
	;	DRIVE SET TO 0 OR 1
	;	CARRY CLEAR TO READ, SET TO WRITE

	;NOTE:	PARAMS (NUMBER OF PARAMETERS) PERMANENTLY 3
	;	L (SECTOR LENGTH) PERMANENTLY $21 (ACORN CODE = 256 + 1)

DISK:	BCS DWRITE
	LDA #RDCMD		;SET INSTRUCTION BYTE TO READ A BLOCK
	STA COMMD
	JMP TODISK		;ALWAYS BRANCH
DWRITE:	LDA #WTCMD		;ELSE SET TO WRITE A BLOCK
	STA COMMD

TODISK:	LDA #0			;MAKE SURE RESULT BYTE IS CLEAR
	STA RWRSLT
	LDA #3			;SET PARAMETER COUNT TO 3
	STA PARAM
	LDA #$21		;SET SECTOR LENGTH TO 256
	STA L

	LDA #0
	STA MEMADD+2		;SET MEMORY ADDR TO RECEIVE BLOCK (IOBUFF)
	STA MEMADD+3
	LDY #HIGH IOBUFF
	LDX #LOW IOBUFF	
	STY MEMADD+1		;4 BYTES = LOW HIGHER HIGHER HIGHEST
	STX MEMADD		;USE ONLY 2 BYTES SO 1ST 2 - LOWEST.

	;READ/WRITE A SECTOR

	LDY #HIGH SECBLK	;GET INSTRUCTION BLOCK 
	LDX #LOW SECBLK
	LDA #$7F		;TELL OSWORD TO R/W A SECTOR
	JSR OSWORD

	LDA RWRSLT		;OK?
	CMP #0
	BNE BADWRT		;NO, FAILED
	CLC
	RTS			;RET OK
BADWRT:	SEC
	RTS			;RET CARRY SET = NO GOOD

	END