[Coco] MPI (was Re: A new idea for a CoCoSDC expander)

[tim lindner]

On Wed, Oct 15, 2014 at 10:23 AM, RETRO Innovations
<go4retro at go4retro.com> wrote:
>  * It looks like it allows hardware selection of 1 of 4 slots by
>    switching the SCS, CART, and CTS lines.
>      o Any other lines switched?

No.

>  * It looks like it buffers the Address and Data lines
>      o Any other lines buffered?

I don't know.

>  * It has a memory register to switch the cart part under SW control
>      o I assume the register will show which cart port has been
>        selected, and allow one to override the switches.
>      o If I am correct, and someone selects another port via SW, do the
>        switches allow one to override the SW selection?

The address for the software switch is $ff7f. Bits 0 and 1 selected
SCS slot. Bits 5 and 4 selecte CTS (and CART) slot.

Write Only.

Writing cause the physical switch to stop working until reset.

>  * Some LEDS
>  * a switch for cart autostart

One improvement I would make is making the CART signal active for all
slots all the time.

If you don't have any auto-starting carts BASIC won't care at all, and
OS-9 already checks for every interrupt source individually.

-- 
tim lindner