[Coco] MPI problem or ...???

[Robert Gault]

Brian Blake wrote:
> Gene,
> 
> The card edges are all clean, and I've cleaned the switch is good
> as I could (alcohol) for now. Jacksonville is the nearest town to me
> that has anything other than a Radio Shack to buy electronics supply
 > stuff and cleaner from, unless I place an order with Jameco or Mouser.
> 
> Anyway, I used the 26-3124 manual for a little diagnostice last night,
 > PEEKing at the value of 65407, and those all came back with the correct
 > values for each slot. The next step was to start POKEing values into
 > 65407 and then PEEKing them to see if the value was the same. So, I
 > used the ones listed in the manual first, 0, 255, 85 & 170. The 0 & 85
 > came back fine, the 255 & 170 did not. So I poked some more values in
 > looking for where the screw up begins. It begins with value 168, which
 > returns 160 when PEEK'ed. Every value POKE'd into 65407 larger than
 > 167 returns a number 8 less thanwhat was POKE'd.
> 
> Example; 
> POKE 65407,170 
> OK
> PRINT PEEK(65407) 
> 162
> OK
> 
> I can't go any further in the process right now due to the MPI not even responding to the presence of a PAK being installed.Even a FDC still boots the the ECB screen. Any other pak, regardless of the slot it's in, causes it to boot only to a green screen.
> 
> Brian

That does not seem normal behavior. With a 26-3024 MPI, all values POKEd 
to 65407 are returned. It really doesn't matter as long as you can 
successfully send any combination of the following bits %00xx00xx to 
65407, but it may be diagnostic of other addressing problems in the MPI.