23 Dec
2005
23 Dec
'05
6:02 a.m.
Other (related) things that I am looking for....
1) The plastic ROM carriers. These are plastic mouldings that you put a
DIP-packaged EPROM into, then crimp the pins over. The same carriers were
used in the Tandy M100, and I think 24-pin versions were used in that
Panasonic hand-held machine that gets mentioned here. I need the 28 pin
ones, I think Molex once made them.
Don't have any spares unfortunately - but FWIW, I believe it is possible to insert
ROMs without them (not great, but possible). I believe I have seen a reference to
this somewhere on the web. 2) Is the PX4
technical manual on the net anywhere (I've found the PX8
one already). The thing I need most at the moment is the pinout of the
cartridge connector. I have a 3rd party 512K (!) RAMdisk module there
which doesn't seem to work.
I'd be interested in any of this info as well. The ROM sits in the second half of the address
space (it's an 8K ROM,
27C64, and it's enabled when A15 is high. It's ghosted 4 times). If this
is like a 68xx, I would expect vectors at the very top of the address
space, with the highest one of all to be the reset vector MSB first.
This ROM contains what looks like code in the first half or so. Then a
large block of FFs. And then the vectors. The very top one is 'E000'
which would point to the first byte of the ROM. Most of the others are
EExx, again in the 'code-like' part of the ROM.
I agree - this sounds like a 68xx architecture. I don't have a Hitachi data book handy, although I
know there are some
"somewhere" in the workshop - I'm guessing that this is a second-source
of a Motorola 6803, which is essentially a ROMless 6801, which is a
slightly enhanced 6800.
It is a much enhanced 6803 I think. The 6303X has quite a bit of on-chip
I/O (including a serial port, 2 counter/timers, etc). But fortunately for
me it is ROMless.
E000 7E E0 00 2 JMP *
E003 01 3 NOP
Thanks... I spent a bit more time on it this afternoon.
I desoldered the '138 address decoder and fitted a socket (it's a normal
PTH DIL package). Bent out the pin that would select the RAM, and tied
that pin on the socket high (thus disabling the on-board RAM). Then
soldered a 6116 DIL pacakge on top of the EPROM with the WE/ and CE/ pins
bent out. Connected those to the Wr/ line and the output of the address
decoder. No change.
I then pulled that kludge and the disk controller chip. At this point the
only active thing on the bus was the processor (RAM disabled, the other 2
chips pulled). hardwared a NOP (01 hex) onto the data lines. OK, it'll
read that as the reset vector too, but should then execute NOPs through
the entire 64K address spece.
Well, the low 8 address lines count up nicely, the high ones are crazy
(bursts of activity with relaticely long gaps). And the Wr/ line is being
asserted (surely not for a NOP).
I am pretty sure the processor is dead, and have desoldered it (80 pin
PQFP, I only lifted one pad on the board, and that is easy to repair).
So now I am looking for a HD63A03XF (I will check that if anyone thinks
they know where to find one). My junk box does contain an HD63A03XP which
is a 64 pin shrink-DIP. I think it's electrically the same, I might be
able to kludge it in (e.g. by sticking it on top of the FDC chip or
something). All I need to do now is get the pinout of that (I know where
to look) and get soldering... Well, unless somebody knows where to find
the exact replacement.
-tony