[Coco] *SLENB behavior?

[Darren A]

On Thu, Nov 10, 2016 at 8:29 AM, Mark J. Blair wrote:

>
> Program Paks simply connected CART* to Q, and the Multi-Pak MUXed the
> CART* signals from each slot. The MPI also provided a 4.7k pull-up for each
> slot's CART* signal. Either a totem-pole or wired-or driver should be fine
> for CART*.
>
> NMI*, HALT* and SLENB* should be treated as wired-or signals, though, even
> if some contemporary designs got that wrong.
>
>

Yes, the HALT* line is another I forgot to mention.

Although not strictly required in an MPI, I would still recommend any new
design treat CART* as wired-or.  There are those who have long advocated
modifying the MPI to tie all the CART* pins together and remove 3 of the
pull-ups so that interrupts from a serial pak or other device are not lost
when the slot is not active.  Of course you then have to be careful not to
use any auto-starting program paks in the MPI, or put some tape over their
Q or CART* pins.


- Darren