[Coco] Detecting carts

[Robert Gault]

Bill Pierce wrote:
>
> Hi guys,
>   Anyone know of an easy way in "C" (or M/L sub) to detect the presence of certain catridges?
>
> RS Speech & Sound pak.

No idea about most of the paks but this should work with the Speech Sound pak as 
long as no other pak does the same thing.

Two I/O bytes are used with this pak, $FF7D and $FF7E. The latter is used to 
send data to the pak and when read shows the status of the pak. If $FF7E bit 7 
(msb) is 0, the pak is busy processing a command.
With a Coco3 and MPI, $FF7E (for me) is 255 without a S&S pak and does not 
change when POKEd. With a pak present, the following happens.
POKE&HFF7E,0:PRINT PEEK(&HFF7E)
  191

The manual says, "... you should first monitor the status byte to determine 
whether or not the S/SC is ready to accept another character."
Likewise if the status bit is always high after sending a value to $FF7E, you 
should not have an S/SC in the system. The converse result might be a false 
positive.