Path: utzoo!utgpu!water!watmath!clyde!att!pacbell!ames!killer!elg
From: elg@killer.UUCP (Eric Green)
Newsgroups: comp.sys.cbm
Subject: Re: Burst Mode on C-64 ?
Message-ID: <4146@killer.UUCP>
Date: 22 May 88 01:42:05 GMT
References: <4110@mtgzz.UUCP>
Distribution: na
Organization: SciCom Services
Lines: 33

in article <4110@mtgzz.UUCP>, bjh@mtgzz.UUCP (XMRN40000[tls]-b.j.hudson) says:
> I have a 1581 3.5" Drive to use with a C-64. [for Amiga transfers]
> It is capable of fast and burstmode operation with a C-128.
> Has anyone seen the Burst Mode U4 ROM replacement for the C-64 from
> Chip-level Design ?  I thought hardware modifications were required ?
> If it is kernal changes only, might GEOS include C-64 burst-mode in
> their yet-to-be-released 1581 support ?        .....BJ

I suspect that ROM is similiar to the Super Snapshot cartridge from
LMS Technologies, which uses a software fastload/fastsave routine
(basically, treating the 1581 like a giant 1541 with more tracks/sectors). 

To do true fast and burst mode operations, you need hardware modifications. In
particular, you need a 6526, and you need bus buffer chips for turnaround of
the 6526 shift register. You can grab the 6526 shift register pins off of the
user port, and you need one data line for the turnaround. Then you need a
replacement ROM to drive this hardware... actually, the software is the
hardest part (most folks who do this sort of thing blow off the cassette
routines to make room in the ROM for whatever). Commodore never did document
the serial protocol, as far as I know, except for some cryptic waveform
diagrams in the back of the C64 PRG. With that diagram, and the disassemblies
in the Abacrap books, you can functionally duplicate the protocol, but,
beware, there's weird timing "gotcha's" all over the place....

I think there is someone who REALLY has burst mode, out there on the market at
this very moment... but, don't ask me who or where. With the dwindling sales
and availability of the C-64, I'm beginning to believe the people who say "The
64 is dying! The 64 is dying!".

--
    Eric Lee Green                     {cuae2,ihnp4}!killer!elg
         Snail Mail P.O. Box 92191 Lafayette, LA 70509              
"Is a dream a lie that don't come true, or is it something worse?"