Re: Fast Serial Detection (was Re: Disk drive timing)

From: Ojala Pasi 'Albert' (
Date: 1998-08-24 22:57:48

Some background: I'm updating my C64 Burstloader routine.

> C128 sends a fast byte, toggling the SRQ line eight times, with the
> ATN line low.

This I knew, or at least guessed. The loader sends a byte to
flag to the drive that we can indeed synchronous serial.
But, I'm sending it before anything else is done, no device
is accessed, and it doesn't seem to matter.

> and respond with a fast acknowledge.

I found the relevant part of the C128 ROM code. The detection
is in SECOND (executed as part of CHKOUT):
.$e3b6	pha			; [ $48 ]
.$e3b7	lda $dc0d		; [ $ad $0d $dc ]
.$e3ba	and #$08		; [ $29 $08 ]
.$e3bc	beq $e3c3		; [ $f0 $05 ]
.$e3be	lda #$c0		; [ $a9 $c0 ]
.$e3c0	sta $0a1c		; [ $8d $1c $0a ]
.$e3c3	pla			; [ $68 ]

The problem now is: the C64 ROM clears $DC0D status in
SECOND.. I would need to duplicate huge amounts of code
just for fast serial capability detection.

Well, actually, there is a way to get over this: I can
use the other CIA i.e. the other synchronous serial port..

Thanks anyway for the info, although it didn't help much.

"The third principle of sentient life is it's capacity for
 self-sacrifice. For a cause, a loved one, for a friend."
	-- Delenn to Draal in Babylon 5:"A Voice in the Wilderness #2"
This message was sent through the cbm-hackers mailing list.
To unsubscribe: echo unsubscribe | mail

Archive generated by hypermail 2.1.1.