28 Nov
1998
28 Nov
'98
11:07 a.m.
On Mon, 23 Nov 1998, Ethan Dicks wrote:
There is that big edge connector on the side of the
static PETs (it was
two seperate pin connectors on later PETs). All the signals you need for
RAM expansion are there.
Yup, you're right. I didn't look at the pinout for that before posting,
I just assumed that I wouldn't be able to access the first 8K of addresses
from there, because it would conflict with the chips on
the motherboard.
There are 12 address lines and 10 select lines.
It would be aesthetically preferable to mount this thing internally via
the chip sockets, but with the edge connector I could expand the PET's RAM
to the max. And it would sure beat that hideously huge 16K RAM expansion
via the PET-to-S100 bus adapter, with its own huge power supply. :)
For maximum preservation, I'd consider pulling all
the 6550's out of the
board and sticking them in a bag. Then, wire up a 6264 (or 62256!) to a
small board after finding a suitable connector. I expect the pinout to
be on ftp.funet.fi, but if it isn't, I can dig out my PET schematics.
If I still had my old 4K PET, I'd build one, too.
I've got the pinout in my "An Introduction To Your New PET Personal
Electronic Transactor" manual. :) According to the bottom of page 23 of
this booklet (I'm going to try to reproduce it as closely as possible
here, for the fun of it):
=========================================================================
MEMORY EXPANSION
40 positions, 80 contacts edge card connector with .1" spacing. No keys.
Top side at connector (B1-40) is grounded.
___
A1 A0 A11 A10 A21 SEL 6 A31 NC | TYPICAL
___ | CONNECTOR
A2 A1 A12 A11 A22 SEL 7 A32 NC |
___ | Sylvania
A3 A2 A13 NC A23 SEL 9 A33 BD0 | 6AD0-40-1A1-01
___ |
A4 A3 A14 NC A24 SEL A A34 BD1 | Viking
___ | 3KH40/1JN5
A5 A4 A15 NC A25 SEL B A35 BD2 | 3KH40/9JN5
___ |
A6 A5 A16 SEL 1 A26 NC A36 BD3 | Sullins
___ ___ | ESC-40-DREH
A7 A6 A17 SEL 2 A27 RES A37 BD4 |
___ ___ | Cinch
A8 A7 A18 SEL 3 A28 IRQ A38 BD5 | 251-40-30-410
___ ___ |
A9 A8 A19 SEL 4 A29 B02 A39 BD6 |
___ ___ |
A10 A9 A20 SEL 5 A30 R/W A40 BD7 |
___
Address selects are decoded in 4K blocks, i.e., SEL 1 selects $1000-1FFF,
___
SEL B selects $B000-BFFF.
=========================================================================
(I especially find it cool that they list various part numbers for the
connector. :) )
I just noticed for the first time (!) that the "PARALLEL USER PORT" has
pins labeled "T.V. Video", "T.V. Vertical", and "T.V.
Horizontal"! Has
anyone actually connectd a TV or external monitor to a PET?
You shouldn't have to build a clip-on, but if you
did, there's nothing
to keep it from working.
How would I select memory block 0 without plugging into the motherboard
somewhere?
You can get all the data bits from two sockets, and
all the address bits
from one socket, plus the additional bits from somewhere else. Remember
that part of the logic in the PETs decodes the A8-A11 lines to chip
selects. You need the original address bits, not the decoded ones.
I guess it would be better (easier) to use the edge connector.
-ethan
--
Doug Spence
ds_spenc(a)alcor.concordia.ca
http://alcor.concordia.ca/~ds_spenc/