[Coco] MC6847 External Character ROM

[Zippster]

Well, I think I’ve found an abundance of unused locations if I’ve read the SAM
datasheets, CoCo2 memory map and schematic correctly.  96 unused addresses
listed as ‘reserved for future use or special io’ (FF60-FFBF).
They don’t seem to be used by either the 74LS783 or 74LS785 SAM versions,
so if they do actually light up y7 as they should on the 74LS138 (IC11) I can
use them for all kinds of stuff.

- Ed
 
> On Jan 22, 2015, at 10:24 PM, Zippster <zippster278 at gmail.com> wrote:
> 
> I rethought how I might do this.  I guess I’d only need 3 address locations.
> 
> Back to studying the service manual memory map… :)
> 
> - Ed
> 
> 
>> On Jan 22, 2015, at 9:50 PM, Zippster <zippster278 at gmail.com> wrote:
>> 
>> Anyone have any suggestions for memory locations to decode for IO
>> to sich a setup?  Is there any room amongst the IO devices on the main board?
>> I don’t want to interfere with anything.
>> 
>> I’d like to stay away from SCS* and CTS* if I can to avoid conflicting with peripheral cards.
>> 
>> I’m looking for 7 bytes if I can get it.
>> 
>> - Ed
>> 
>>> On Jan 16, 2015, at 8:15 PM, Luis Antoniosi (CoCoDemus) <retrocanada76 at gmail.com> wrote:
>>> 
>>> I a nice improvement would be using SRAM and allowing the coco to change it
>>> on the fly using some port. The SRAM would be dumped from ROM upon reset.
>>> 
>>> Just in case you end up without any other project ;)
>>> 
>>> 
>>> 
>>> Luis Felipe Antoniosi
>>> 
>>> 
>>> 
>>> On Fri, Jan 16, 2015 at 9:02 PM, Zippster <zippster278 at gmail.com> wrote:
>>> 
>>>> The earlier style (USA) CoCo2’s are socketed that I’ve seen.
>>>> A lot of the later (Korean) ones would need a socket installed.
>>>> 
>>>> - Ed
>>>> 
>>>> 
>>>>> On Jan 16, 2015, at 7:49 PM, Allen Huffman <alsplace at pobox.com> wrote:
>>>>> 
>>>>>> On Jan 16, 2015, at 7:42 PM, Zippster <zippster278 at gmail.com> wrote:
>>>>>> 
>>>>>> I’ve got my External Character ROM prototype for the MC6847 working.
>>>>>> There’s a few pics I put up here if anyone is interested in taking a
>>>> look.
>>>>> 
>>>>> 
>>>>> Wow. That takes me back. I need to crack open my CoCo 1 and see what
>>>> model lowercase mod I had in it. It wasn’t the big brand — something
>>>> cheaper… That’s really neat. I think my VDG was socketed on the CoCo 1.
>>>>> 
>>>>> I assume later CoCo’s had it soldered to the motherboard? Soldering
>>>> would be required to install?
>>>>> 
>>>>> --
>>>>> Allen Huffman - PO Box 22031 - Clive IA 50325 - 515-999-0227 (vmail/TXT
>>>> only)
>>>>> Sub-Etha Software - http://www.subethasoftware.com - Established 1990!
>>>>> Sent from my MacBook.
>>>>> 
>>>>> P.S. Since 4/15/14, I have earned OVER $600  in Amazon gift cards via
>>>> Swagbucks! Use my link and I get credit:
>>>>> http://swagbucks.com/refer/allenhuffman
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> --
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>>>> 
>>>> 
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>