[Opendispense] Questions - new memory map

Bernard Blackham bernard@blackham.com.au
Mon Aug 11 04:50:14 2003


Just some questions & notes I'd like to get answered...

To get an extra UART onto the board, the ideas are to put a riser
board from the EPROM socket. The socket only has A14-A0, and is
enabled when A15 is high (ie, $8000-$FFFF). So as I see it, to put
anything else along-side this EPROM would either involve:

 - dividing the usable EPROM in half, assigning $C000-$FFFF for the
   EPROM and addresses between $8000-$BFFF for our extras (the
   UART). This gives us 16k of usable EPROM (still heaps), but
   limits our options for putting in extra RAM and such. Though if
   we're acting as merely an interface (which I hope this first try
   is) this is not a problem.

 - or, a bit of logic to map certain addresses out of EPROM space,
   so we lose a smaller power of 2 of the EPROM, and extra memory
   that may be installed in the future. :)

We also have the problem of the RW' line requiring to be low (R) to
access the EPROM and hence riser board. We'd need to hack the board
and cut some tracks to get around this, which wouldn't be so nice.

I'd be happy for somebody more versed in computer architecture to
point out some other ways :)

As to which UART to choose, are there any pros/cons between them? If
I start writing some code to chat with a 16550A UART, will it be



 Bernard Blackham 
 bernard at blackham dot com dot au