[Coco] Fest Weekend

[coco at yourdvd.net]

Back then, I was not familiar with the HC designation, other than
HIGHspeed CMOS - I didn't really think it would work but I was playing.
It worked most of the time without a multi-pak or other device in the
pak slot of the coco, but with a multi-pak or disk controller,
operation was intermittent. I know a lot more these days than I did
back then :-) Since I was replacing the 245, I wanted a faster part
(and Marty Goodman had suggested possibly using F245's in the CoCo and
Multi-Pak, so I experimented around a bit.). I made a 256k battery
backed ramdisk back then that was compatible with disto's
RAMdisk(addressing wise). If I could find a 1986 DISTO catalog listing
the memory map I was going to make a 1meg battery backed setup :-) I
love to design and build things and the tools available today are so
much more advanced than I had then.

I have considered the possiblity of using latches to latch the GIME
address lines with RAS and CAS to generate a 256k address bus, using
the WE0 and 1 signals to generate the extra address line (since the
CoCo is designed for two banks of 256k, I would need to generate the
upper address line from the bank signals) and seeing just what it would
take to get a 512K static RAM to function in the CoCo 3 as a 512k
upgrade, but I;ve only just started looking into this. Does it sound
feasible or am I wasting time?

---robert


> -------- Original Message --------
> Subject: Re: [Coco] Fest Weekend
> From: jdaggett at gate.net
> Date: Thu, April 05, 2007 2:36 pm
> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> 
> On 5 Apr 2007 at 5:51, coco at yourdvd.net wrote:
> 
> > I found out my CoCo didn't like an
> > 'HC245' but it could digest the 'F245 and 'LS245 (original part) - so
> > by next visitation, we were ready to kill some more evil space drones
> > :-)
> 
> HCMOS devices are not guaranteed to be compatible with LS TTL devices or 
> NMOS devices. The MC6809E is NMOS and can drive one TTL load. There is a 
> range of about 0.7 VDC that there can be an incompatiblity. Vinput
> high for the H 
> C245 is 3.15VDC. The minimum Voutput high for the MC68B09E is 2.4VDC. If 
> the MC6809E is loaded enough, the HC245 will never see a logic "1" at
> the 
> inputs. LSTTL and Fast TTL logic will work. ALso HCT logic will work
> with NMOS 
> devices. 
> 
> Also TTL/LSTTL  have higher noise immunity than HCMOS and CMOS logic. 
> 
> 
> james  
> 
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