Data on Motorola 68705u3

That's one of the old (mid-1980s) HMOS parts, you're not likely to find anything useful these days. If you find someone with an old Motorola Microprocessor/Microcomputer data book set (two volumes) from that era, it will have the data sheet. What else are you looking for?

I've got an old coin-op game that runs on one, and I need to write my own code for it. My understanding is that I'll have to start from scratch as on this chip, there's no way to read out the existing code.

...although I've read that some of them support a trick where you boot it up off serial data loaded into RAM which can then read the ROM data out, but I'm not sure if my device supports that. It's a 68705U3S.

Mainly, I need:

- The schematic for the EPROM transfer programming circuit.

- An instruction set reference.

- General data about the registers and operation.

I've got a pinout, basic memory map, and assembler.

-Paul

Hmm, Hitachi 2nd sourced the 6805 as well as doing their own variants (6305). That might give you a place to look for more info. I've got an old 8/16 bit data book, but no EPROM versions, so I can't help you with the programming/security.

Usually they were used to scramble control inputs. The idea was that if you couldn't read the chip out, you couldn't duplicate the chip for clones. That slowed the clone makers down a day or so. As I recall, there was some kind of bug in the 68705 security. I don't remember what it was, but probably involved internal/external memory modes. (Boot in external mode, load "trojan" into ram, flip to internal mode? I guessing.)

Which game? (Probably Taito.)

--
Ron Sharp.

A little more research and I've found the 68HC705SR3 which appears to be the modern equivalent of the 68705U3. It looks like it has exactly the same pinout and functions. The only difference I've found so far is that the memory map is slightly different and trades a little ROM for a little more RAM.

Anyone know if there are any problems using this chip as a drop in replacement?

The data sheet does have an instruction set reference, and I'm assuming it's the same set as the 68705U3 so I've got that covered.

-Paul

The whole set of manuals and the appnote on self-programming used to be available from motorola not so long ago in PDF form.

Goto

then find literature distribution center ->

archived documents and search for the docs you need:

M6805UM - user manual for the whole family MC68705R3 - data sheet on P/R/U3 AN857 - appnote on self-programming

... or post another message here if you need more help.

I've a set of the manuals which you're welcome to for the cost of postage. I also have two programmers and some windowed and OTP 68705R5 devices which we no longer use.

If you're still looking, I happened across a programming circuit for a

68HC705C8 in the April/May 1992 issue of Circuit Cellar. I checked had no luck with the search for an ecopy. (Hey, it was only 11 years ago.)

--
Ron Sharp.

You can get scanned images on CDROM #1. See

-- Dave Tweed

I figured there were probably CDROM archives, but I didn't bother looking because (a) I didn't need the circuit (b) I had the printed copy anyway. :^) Oddly enough, 68HC05 circuits keep popping out at me -- I was organizing magazines and *bam* Micro Cornucopia #49, Sept/Oct 1989 lands in front of me. I was looking for a simple SIMM refresh circuit, but what the hey..

--
Ron Sharp.

My 68hc705c8a programmer with all the source code is on my web site at

Ian

--

Thanks everyone so much for all the help!

I may have more questions later, but I've got everything I need to get started now. Derek Weston gave me a good deal on his data books, Motorola 68705 development/debugger board, a bunch of 68705s, and some other useful gear.

Also, I did find most of the info on the Motorola website from Grzegorz' suggestion. I had a little trouble getting there, so here's specific instructions for future reference:

Go here:

Select - Design Support, then Select - Documentation then scroll down to the bottom of the page, and Select - Literature Distribution Center Archived Documents Type the the document code (ex. M6805UM) in the "Document Number" box and Select - Search, the PDF files can be viewed and downloaded from here.

And again, the document names are: M6805UM - user manual for the whole family MC68705R3 - data sheet on P/R/U3 AN857 - appnote on self-programming circuit

-Paul