[Coco] MCM68766

[Joe]

Yes that's what I was coming up with, One the other hand I know I was 
running a coco3 with Ados 3 and a 68766 back in the day. I also know the 
fastest they ever made these chips was 300ns. Sooo with a little luck I can 
probably find a couple that will run fast enough. Got 15 to play with.
As for programming them, Yes any programmer circa late 80's early 90's will 
work, Its just finding one with the software that will work under NT. There 
are some recent ones that will support it but they are like $500.00. I'm 
going to homebrew route and build my own. Would anyone else be interested in 
building one assuming I get it working? I've come up with a really small 2 
chip design that works on paper at least. I'm talking just 68766 support and 
breadboard type of thing.
BTW while I'm asking stupid questions anyone know the diff between a 68766 
and a 68764?? The spec sheets seem to indicate they are identical AFAIK.
thanks


----- Original Message ----- 
From: <jdaggett at gate.net>
To: "Mike Pepe" <lamune at doki-doki.net>; "CoCoList for Color Computer 
Enthusiasts" <coco at maltedmedia.com>
Sent: Sunday, July 13, 2008 11:21 PM
Subject: Re: [Coco] MCM68766


> Mike
>
> You need 250nS access time for the ROM memory for the Coco to run at
> 1.78MHz period. On the ROMs and static ram the access time and the cycle
> time are equivalent. The maximum access time is the fastest that the ROM
> can operate at. The inverse of 350nS is about 2.85MHz. Since the Coco
> uses IDMA to access both data and video memory, at 1.78MHz half of the
> 560 nS cycle time is used to access data/program memory. The other half is
> used to access video memory.  That is 260nS for a read cycle at 1.78MHz.
> This means in a Coco system the fastest clock for 350nS ROMs is about
> 1.425 MHz. Like I said before they work fine with the clock at 0.89MHz
>
> Motorola speced that part at 250nS and 350nS. If it works reliably at the
> faster speed, it would have been marked that. Even if it had an access 
> time
> of 300nS, which is faster than 350nS, it is still to slow for 1.78MHz 
> clock.
>
> james
>
> On 13 Jul 2008 at 14:47, Mike Pepe wrote:
>
>> > -----Original Message-----
>> > From: coco-bounces at maltedmedia.com [mailto:coco-
>> > bounces at maltedmedia.com] On Behalf Of jdaggett at gate.net
>> > Sent: Sunday, July 13, 2008 11:46 AM
>> > To: Joe; CoCoList for Color Computer Enthusiasts
>> > Subject: Re: [Coco] MCM68766
>> >
>> > Joe
>> >
>> > They are useful as long as you keep the Clock at 0.89MHz. They are
>> > to slow for the 1.78MHz clock. As for programming them most older,
>> > 80's vintage, EPROM programers will suffice.
>> >
>> > james
>> >
>>
>> Keep in mind that this rating is the maximum guaranteed access time.
>> It's quite possible the device may be faster-it's just guaranteed not
>> to be any slower.
>>
>> Regardless, though, it'll work at the stock clock rate, as pointed out
>> above.
>>
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