How to write/read sector(s) to/from the Tandy DVI.

RWSCTR	E3C0	This routine will handle all handshaking and data transfer
		required to transfer data sector-by-sector between the
		Model 100 and the Tandy DVI.

Entry conditions:  Device number (00 or 01) should be at $FC89
	Flags:		Carry set - read
			Carry clear - write
	Registers:	A = number of sectors
			B = track number (00 - 27)
			C = starting sector number (01-12)
			DE = start RAM address
				- read - destination for data
				- write - start of data to write

Exit conditions:   Zero flag set - data transfer OK
		   Carry flag set - error byte in A (except 02)
		Error bytes: 02 - Drive Error (exits to BASIC "Illegal
					Direct Error")
			     03 - Write-protected
			     04 - R/W Error
			     06 - Undefined Error

Sample calls--

Read a Sector...

RWSCTR	EQU	0E3C0H
DVNMBR	EQU	0FC89H	;Device number stash
	MVI	B,2	;Track number = 02
	MVI	C,1	;Sector number = 01
	LXI	D,0FCC0H ;Destination address (prev screen memory)
	MVI	A,0	;Drive 0
	STA	DVNMBR
	MVI	A,01	;# of sectors = 1
	ANA	A	;Clear Carry flag.. read a sector
	CALL	RWSCTR
	JC	ERROR	;Add your own error-handling routine
	RET

Write a sector... Same as above, but add STC instruction after ANA A.

	This should enable you to read and write sectors to the DVI from
machine language.  If you have any problems or suggestions, leave me a
message or MAIL (preferably MAIL).
 
	Dave Newman [76656,2526]
	DaMN Software, Uninc.
	946 South 12th
	Lincoln, NE 68508