[Coco] CoCo 3 memory expansion questions

[Neil Cherry]

On 2/3/19 11:50 AM, RETRO Innovations wrote:
> On 2/3/2019 9:38 AM, Frank Swygert wrote:
>> I don't think you can use ANY memory expansion at all.
> Um, I'd say that is a pretty strong statement, and likely to be false.
>> The Sardis ST2900
>> appears to be made from the Motorola 6809 spec sheet, much the same as the
>> CoCo 1 and 2.
> 
> As such, something like CoCoMEM Jr (a 2MB RAM expansion under development for the CoCo1/2) 
> should work in this unit, along with similar units.
> 
> In this particular case, it looks like the Jr unit would need to be modified, as the 
> ST2900 uses a 6809, not a 6809E, so the pinout has to be adapted.  Not a huge deal.

I think that was pretty much a few TTL chips to get the correct signals.
Things like Rd or Wr late. The basic idea being that the Clock would still
be derived from the xtal and the control signals would really happen until
the bus and data were stable. I worked with an engineer who knew those in
his sleep. Of course I haven't played with it enough to recall the details.

-- 
Linux Home Automation         Neil Cherry       ncherry at linuxha.com
http://www.linuxha.com/                         Main site
http://linuxha.blogspot.com/                    My HA Blog
Author of:    	Linux Smart Homes For Dummies