Re: 1541 clone help needed

From: Jim Brain <brain_at_jbrain.com>
Date: Fri, 17 May 2019 20:43:13 -0500
Message-ID: <637edc6d-d337-d4ef-7bc2-0ea3063522b6_at_jbrain.com>
On 5/17/2019 8:49 AM, Martin Hoffmann-Vetter wrote:
> Hello Jim,
>
>> Many clone drives used a direct copy, an obfuscated copy, or a
>> marginally modified 1541 drive ROM to power their units.
>>
>> Someone provided me a BlueChip/Amtech drive ROM, and I finally had a
>> chance to look at it.  It's a 16kB ROM, and the e000 looks almost
>> exactly like the 1541 -05 or -06 ROM.  The $c000 portion is radically
>> different, or at least looks different at first glance.  But, given
>> the minimal changes in the upper half, I burned a copy and
>> successfully booted a 1541 with it.  Thus, I'm wondering if someone
>> could help me decipher: What is indeed different (of note) in the
>> $e000 rom?
>> Why the $c000 rom is so different, and does it need to be that way
>> (or, can I just replace it with a 1541 $c000 ROM image)?
>> The files, if folks are interested, are at:
>> http://www.jbrain.com/incoming/BlueChip/Amtech_BlueChip_ROM.BIN
>> http://www.jbrain.com/incoming/BlueChip/Amtech_BlueChip_ROM_c000.BIN
>> http://www.jbrain.com/incoming/BlueChip/Amtech_BlueChip_ROM_e000.BIN
>> The latter two are just the first split in half.
> It's the same as the roms of Rapid Access FD148. So, i've disassemled some time ago.
>
> Look at http://mhv.bplaced.de/cbmdos/Amtech_BlueChip_ROM.ZIP. Your will find Rapid Access FD148.s and dos2.6_1541_Rev2.s to compare. This rom based von revision 2. I would say that's equal. Only some operation sequence are changed. Any loops are changed to use an index minus/plus one. But both version do the same.
>
> Martin
>
>
Thanks.  I was attempting to disassemble it last night, but it was going 
to take some cleanup.

Given Pete's response about putting a JD ROM in and the thing refusing 
to work, does anyone on list have the drive and would be willing to 
test?  I've got some folks wanting a JD ROM, and I'd rather just suggest 
a 1541C ROM if it would work.

Jim

-- 
Jim Brain
brain_at_jbrain.com
www.jbrain.com
Received on 2020-05-29 22:05:19

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