[Coco] SDC's fixed; but not sure why? DANGEROUS ?

[William Astle]

Having a Disk Basic ROM work properly under the FIRQ based autostart 
gimmick would be accidental. They are not meant to be started that way. 
As Art says, they are meant to be entered at $C002 instead of C000. The 
FIRQ based autostart launches ROMs at $C000 after doing some 
re-initialization of the system. Further, it launches ROMs in ROM mode 
which will mess with the Coco3 SECB stuff.

On the other hand, ECB detects the presence of a Disk Basic ROM based on 
the 'DK' signature at $C000. If it find it, it launches the Disk Basic 
ROM at $C002 immediately after ECB has initialized all its stuff. That 
also means the system will be in RAM mode on the Coco3.

In other words, you should never have a Disk Basic style ROM using the 
FIRQ based autostart. Other ROMs, sure. But never a Disk Basic style ROM.

I think Art is correct on the 6309 illegal instruction. The 'K' in the 
'DK' signature is an illegal instruction even on the 6309. That will 
cause it to vector to $0000 on a stock Coco3 (the value at $FFF0 which 
comes from the internal ROM).

On 2018-07-09 09:58 AM, Arthur Flexser wrote:
> My guess would be that one of your CoCo 3s has a 6309 and the other has a
> 6809.  Executing a disk ROM cartridge at $C000 instead of $C002 will likely
> result in one or more illegal 6809 instructions being executed, which are
> treated differently (error trapped) by the 6309 than by the 6809 (ignored).
> 
> Art
> 
> On Mon, Jul 9, 2018 at 11:45 AM, rietveld rietveld <rietveldh at hotmail.com>
> wrote:
> 
>> I had all power off.
>>
>> But the strange thing is that the two SDC'S, with the jumper set to AUTO,
>> did work on one of my coco3s,    even though it should not be able to
>>
>> Sent from my BlackBerry 10 smartphone.
>>    Original Message
>> From: coco at jechar.ca
>> Sent: Monday, July 9, 2018 11:35 AM
>> To: CoCoList for Color Computer Enthusiasts
>> Reply To: CoCoList for Color Computer Enthusiasts
>> Subject: Re: [Coco] SDC's fixed; but not sure why? DANGEROUS ?
>>
>>
>> I did not know that you could hotplug a COCO CARTRIDGE under any
>> circumstances. I know you would probably wreck the wreck the CARTRIGE
>> and Probably the COCO ( Especially if it had no "PROTECT" ) if
>> you tryed to hotplug. So what are the rules for 1. Multipacks 2. 90's or
>> Modern Multipack replacements?
>>
>>
>> On 2018-07-06 23:55, rietveld rietveld wrote:
>>> If anyone saw this video they will know that I had trouble with two
>>> SDC'S working on all but one of my cocos
>>>
>>>
>>> https://m.youtube.com/watch?v=RWLI32mXeKQ
>>>
>>> I was at a loss of ideas so I just blindly removed the jumper that
>>> joins the centre (yes that's how we spell it in Canada) pin to the
>>> Auto pin. These pins are supposed to be jumpered to allow the SDC to
>>> run on the coco. I removed the jumper completely and now both SDC'S
>>> auto start to SDCX on powerup.
>>>
>>> Strange but true
>>
>> --
>> Coco mailing list
>> Coco at maltedmedia.com
>> https://pairlist5.pair.net/mailman/listinfo/coco
>>
>> --
>> Coco mailing list
>> Coco at maltedmedia.com
>> https://pairlist5.pair.net/mailman/listinfo/coco
>>
>