jpd@usl.UUCP (James P. Dugal) (10/14/85)
I have just adapted the MF-100 multifunction board for use at memory addresses
at or above 80000. Perhaps this information will be useful to others.
I wanted to use the memory portion of the card as a ramdisk at C0000 - DFFFF.
To have the board respond to these addresses, it is necessary to complement
the address line A19 before it is fed into the decoder chip U60 (a 74S573)
at pin 4. Happily, there is a spare inverter on chip U82 (a 74LS04) that can
be used. I broke the trace at U60 pin 4, and connected the pin to U82 pin 6.
U82 pin 5 is then connected to the broken trace, which is easy to access
at the plated-through hole connected to bus connector A12 (this is address
line A19). The starting address switch settings shown in the manual will now
select the listed address + 80000 Hex.
The board is being used in a Zenith Z-160, which tries to access locations
in the C0000 range when it is cold-booted (looking for a Z319 video card, I
guess). Since the memory has not been initialized, the cold boot will fail
with a parity error message. Thus parity checking should be disabled on the
MF-100 by removing the jumper JP3. An alternative is to initialize the
memory using the ROM monitor (by FC000:0L0,0 and FD000:0L0,0) and then reboot
via ctrl-alt-del.
The MF-100 card is being sold with 0K for $130 by Micro Products International
of Huntington Beach, CA (714-898-0840). It also includes a serial port,
parallel port, game port, and clock/calendar. Software for the clock, ramdisk
(can't be addressed above contiguous memory; I use MDISK.DVD with the
start=c000 parameter) and print spooler (untried) is also supplied.
I knew I could use the 64K RAMS I removed when upgrading to 256K chips!
--
--
James Dugal
Assoc. Dir., USL Computing Center
USENET: {akgua, ut-sally}!usl!jpd
CSNet: DugalJP%usl.csnet@csnet-relay.arpa