Quick survey on equipment

[Allison]

>
>Subject: Re: Quick survey on equipment
>   From: ard at p850ug1.demon.co.uk (Tony Duell)
>   Date: Mon, 23 Apr 2007 23:30:04 +0100 (BST)
>     To: cctalk at classiccmp.org
>
>>   > The problem was that CP/M needs RAM starting at location 0, the
>>   >TRS-80 has the BASIC ROMs there and starts RAM at, IIRC, 0x4000.
>> 
>> Hmm, same problem as the Model III then (ISTR that had its ROM located at 
>> $0000 too, hence the reason for the Model IV).
>
>Exactly. The Model 1 and Model 3 are actually quite similar machines 
>internally, to the extent that a Model 3 ROM set will run on a Model 1 
>(if sutiably addressed). Admittedly the Model 3 makes more use of the Z80 
>I/O ports (almost all I/O on the M1 is memory-mapped for some unknwon 
>reason), but the memory nap, video, etc, are the same.

Maybe because the IO instructions are slow compared to something like 
(8080 neumonics) Mov M,A.  Also since they used a Memory mapped video
that ate 1k of space along with the 12k of rom why not do the keyboard 
that way.

Actually there are quite a few IO mapped ports on the M1 but the 
keyboard and Video are in the memory map.



Allison


>
>The M4 has quite a few changes over the M3. It has the 
>software-selectable memory maps, allowing RAM at location 0 for CP/M. And 
>a much improvded video section with a 6845 CRTC chip (and not a 
>fixed-configuration row of TTL of the older 2 machines) thus giving am 80 
>column text display, etc.
>
>>   >....The second solution was an add-on circuit board....
>> 
>> Hmm, sounds like these are probably going to be as easy to get hold of now 
>> as hen's teeth...?
>
>I don't recall there being any published schematics for them either, so 
>if you want to build one you'll have to design it yourself.
>
>> 
>> Think I'll just get a Z80 Second Processor for my Beeb instead (far less 
>> hassle).
>
>I didn't think those were _that_ common...
>
>-tony