| Welcome to cbm264 Software! |
| * These pages will open in a new browser window. Close the window to return to www.cbm264.com. |
Adding 3+1 ROMs to the C16
by Mike Naberezny (Mike@MikeNaberezny.com)
Originally presented on www.6502.org
"I had intended on building a printed circuit board version of this,
however since I just thought up the idea and didn't know of anyone who had
done it, I handwired it to see if it would work. This is what you see.
Someday I'll probably build a PCB for it, but if I do I'll put some other
goodies on it as well.
"The 74LS139 was desoldered off of the board and a socket installed in its
place. The ribbon cable plugs into it and the the '139 now resides on the
daughterboard. The daughterboard, located on top of the RF modulator,
uses two additional chips to complete the address decoding.
"The original KERNAL and BASIC ROMs are removed and no longer used. These
two 16K ROMs are burned into a single 32K EPROM. The 3+1 software, also
on two 16K ROMs, are burned into another 32K EPROM. On each EPROM, chip
select and the highest address line are bent up ninety degrees. This is
because the C16 motherboard is not modified under the ROM sockets; this is
a plug-in upgrade (except for socketing the '139). The EPROMs are
installed in the sockets and four wires connect the lines back to the
daughterboard.
"Of course, the 3+1 software isn't much use on a 16K machine, so this
motherboard has also been upgraded to 64K. The two 74LS257A multiplexers
were removed, the necessary traces cut under them, and then reinstalled.
The 4164 DRAMs were replaced with 4464's, and the additional wiring is
done under the board.
"Best Regards, Mike"