MC68701 Controller

Hi all,

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?

Reply to
Stefan Huebner
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On Sat, 05 Jun 2010 03:24:15 +0200, Stefan Huebner put finger to keyboard and composed:

0xB = 0b1011

Shouldn't A14 and A13 be swapped?

- Franc Zabkar

--
Please remove one 'i' from my address when replying by email.
Reply to
Franc Zabkar

Franc, you are GREAT!

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:

Reply to
Stefan Huebner

Hi all,

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

Reply to
teginyucelmayadagli

First thing to do is decide whether you can read the code. 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.

Reply to
mike

Unlike other old 687xx parts, the EPROM programmer program is in an 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 snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

Reply to
Mark Zenier

In an act of shameless self promotion I just wanted to let you know that I offer reading and programming services for the MC68701 and MC68705P3/R3/U3. See my web site at

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