membership card + elf2k ROM ?
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.
Could I piggy back an elf2k ROM with the RAM chip, do something with pin
20 to select the ROM for 0x8000? Are there any other issues that might
prevent me from using a membership card with an elf2k ROM? Has anyone
else done similarly?
Mark G. Thomas (Mark@...)
- Mark G Thomas wrote:
> So, I'm putting together a membership card in a slightly larger case thanThere are several ways you can do this.
> 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.
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