R60
Listing 2. Modified select-disk BIOS routine that also swaps
logical drives B and C.

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ISELDK:	LD	HL,(DRVEC)	; Get drive vector
	LD	A,16		; Get 16-drive into B
	SUB	C
	LD	B,A
ISELDSK1:
	ADD	HL,HL
	DJNZ	ISELDSK1
	LD	HL,0		; Value for invalid drive
	RET	NC		; Return if invalid drive

	LD	A,C		; Get disk requested
	CP	2		; See if it's C:
	JR	NZ,ISELDSK2	; Skip if not
	LD	C,1		; If so, change to B:
ISELDSK2:
	CP	1		; See if it's B:
	JR	NZ,ISELDSK3	; Skip if not
	LD	C,2		; If so, change to C:
ISELDSK3:
	LD	A,27		; Now log in drive
	JR	DOBIOS