[Coco] 6809 to 6309 Switcher Help...Semi Related: ROM switcher ?

[RETRO Innovations]

On 11/20/2020 10:01 AM, Bruce W. Calkins wrote:
> It can be done.  One pin of each ROM would need to be switched.  So 
> they could easily be piggybacked.  Optionally a larger EPROM would be 
> burned with the appropriate address line(s) switched.  It has been a 
> while, I would have to look at the pin-outs to reremember which pins 
> need to be involved.

It's pin 1 of a 27C512.  (A15).

  * Grab an image of both 32kB EPROMs, concatenate them together into a
    single 64kB ROM image, and then burn to a 27c512 EPROM.
  * Then, cut pin 1 off, leaving just enough to solder a wire and
    resistor to.
  * Grab a resistor (4.7K to 10K is fine) and solder one end to pin 1. 
    Solder the other end to pin 28 (+5V)
  * Grab a 2 conductor wire.  Solder one end of 1 conductor to pin 1. 
    Solder the other conductor of the same end to pin 14 (ground)
  * At the other end of the wire, solder both conductors to 2 legs of a
    single pole, single throw switch.
  * Mount switch on CoCo or let it hang outside the case (your choice).
  * Then, flipping the switch 1 way gives one ROM, the other way gives
    the other ROM.

Jim