[Coco] 6 Chip ^809 Computer -> Kipper SBC

[Stephen H. Fischer]

----- Original Message ----- 
From: "RETRO Innovations" <go4retro at go4retro.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Saturday, March 14, 2015 10:37 PM
Subject: Re: [Coco] 6 Chip ^809 Computer -> Kipper SBC


> On 3/14/2015 8:14 AM, Gene Heskett wrote:
>> Jim, this exactly the thinking that resulted in the coco shipping with an
>> address decoder that only decoded in slices $20 wide.  So the on-board
>> I/O used up $40 bytes when in fact it needed $08 bytes to service the
>> two PIA's.
> Which is why Tandy put the !SLENB signal on the bus.  By using it and a 
> decoder, you can make the onboard PIAs only respond to $08 bytes of 
> address space.
> 
> Jim

Tandy EEs must have been listening like I was when the EE professor taught us about "Don't Cares".

Yes "Don't Cares" were part of my training. I remember that class quite well.

So it is no surprise to me that $40 bytes were used when $08 would do.

SHF