Mark G Thomas wrote:
> So, I'm putting together a membership card in a slightly larger case than
> an altoids tin, and I got to thinking it sure would be nice if it had a
> ROM monitor, and I could put a serial port on my enclosure.
There are several ways you can do this.
1. You can load a program into RAM, and maintain power to keep it there.
2. Same thing, but use a nonvolatile RAM, like one with the piggyback
lithium cell, or a ferroelectric RAM. This way you don't need to
3. You can build a ROM board, as designed by Richard or Herb Johnson.
These are basically a binary counter to provide sequential addresses
to a PROM or EPROM. Plug it in to the 25-pin front socket, and its
contents is automatically loaded into RAM.
4. Get a 2nd Membership Card (rev.D or later). There are provisions to
stack the two, with a ROM on one board and a RAM on the other board.
Now you have both ROM and RAM, as well as a second I/O port.
5. I'm sure there are other ways as well. I can imagine piggy-backing
two memory chips (one EPROM, one RAM), with one of the address lines
used to chip-select between the two.
The most dangerous enemy of a better solution is an existing one that
is just good enough. -- Eric S. Raymond
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm