MC68701 Controller
Stefan Huebner
Does anyone still know the MC68701? It's the EPROM version of the 6801.
It offers a Mode 0 which allows for reading and writing the internal
EPROM - not like the Hitachi 68xx which can be read and written as 27256
with an appropriate adaptor, this beast needs a monitor program run in
mode 0 to work on the EPROM.
Now I have one 68701 left with some special code in it and need to
reverse engineer the serial protocol it talks (there are some codes sent
to another system which couldn't be simulated once we tried, so I need
to know which condition leads to sending them).
I built a small circuit with the 68701, a HCT573 latch, a 2764 with
Motorolas ProBug monitor in it and a HCT138 wired somewhat weird - A12,
A14 and A15 go to A,B and C, while A13 goes to /G1, /G2 is grounded and
G3 goes to E. Which makes a chip select for B000:BFFF on Y7.
But I cannot get the damn thing reading from my EPROM! The data sheet
says clearly that in mode 0, the reset vector is BFFE:BFFF. But my 68701
will never read from any Bxxx addresses for a single cycle!
Switchhing it to mode 2 or 4 for example works. Opposite to the 6801,
which fetches the reset address from FFFE:FFFF also in mode 0 (but then
allowing those two addresses to be supplied externally for 2 E-cycles)
the 68701 should read from my EPROM on Bxxx.
Anyone an idea?
Franc Zabkar
<ste...@huebner-informationselektronik.de> put finger to keyboard and
composed:
>I built a small circuit with the 68701, a HCT573 latch, a 2764 with
>Motorolas ProBug monitor in it and a HCT138 wired somewhat weird - A12,
>A14 and A15 go to A,B and C, while A13 goes to /G1, /G2 is grounded and
>G3 goes to E. Which makes a chip select for B000:BFFF on Y7.
0xB = 0b1011
Shouldn't A14 and A13 be swapped?
- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
Stefan Huebner
I will go and bite my very own a** on monday.
I wrapped the circuit together on veroboard somewhen in the evening and
now I hope that I actually made the mistake I wrote below.
Ten years ago I had some colleagues who would have looked at my circuit,
as the one who built it is always somewhat blind. They would have
started smiling, tell me, and then we'd have gone for a coffee
downstairs at the other workshop. It's about time I start looking for
new rooms and some colleagues who work with me.
Franc Zabkar schrieb:
teginyuce...@gmail.com
i want to copy a mc68701 mcu to another mc68701 cpu. how can i do this?
I googling the web but many links are dead.
please help.
regards
mike
If the chip has a code protect bit, you probably won't be able to.
Then you need some means to program it.
I scanned the datasheet and was unable to
determine whether the chip is protected (in the time I was willing to
devote).
I also have an old programmer of that vintage that doesn't
claim to support the chip.
Unless you're trying to fix an irreplaceable device,
I'd give it up.
Mark Zenier
external rom and the chip is run in expanded mode using a development
board. The program and circuit for a basic programmer module is in a
motorola ap. note. (I think it's in a couple of ap notes, as they came
out with a revised version. There should be a reference to the ap. note
number in the data sheet).
There's no code protect in a '701. There's 8(?) different modes the
chip can get set into during reset, with different memory maps for all
the resources. The 68701 is almost the same as a 6801/6803, replacing
the mask ROM with EPROM and the extra programming hardware (a control
register) and (as I remember) a mode that picks a different reset vector
to an address range in external memory for the programming program.
As I remember, after 30 years, the basic programmer used a regular
EPROM as the input, so you would need another program to read out
the existing chip.
Mark Zenier mze...@eskimo.com
Googleproofaddress(account:mzenier provider:eskimo domain:com)
