MOSTEK 3870. I want info for emulation

[grzeg]

I know this is not 6502.
I want to emulation MOSTEK 3870.
Maybe someone knows how to use a pin TEST, Port 5 and Port 4 for read or debug the ROM?

[BigEd]

Hmm. Datasheet needed. Note that this is a MOSTEK part - not MOS. Two different companies.
"The 3870 (MK3870) 8-bit microcontroller is a single chip implementation of Fairchild F8 (Mostek 3850)"
There are some docs at http://www.textfiles.com/bitsavers/pdf/fairchild/
but it looks like TEST mode is not documented...

Some people did succeed in dumping the ROM from a 6500/1 - see
http://e4aws.silverdr.com/hacks/6500_1/
"The long believed to be inaccessible for mortals 6500/1 firmware of the VC-1520 device has been retrieved!"

It's a different chip, but it might give clues as to what you'll need and what to try.

[seanriddle]

I have dumped the ROM from several 3870s using the test pin. It's a little complicated; a few data sheets go into some detail. When you put around 7V on the test pin, the ROM is disabled and you can input opcodes on port 5. When you put 3.5V on the test pin, the ROM is enabled and the databus is output on port 4. In both cases, /STROBE becomes an output, similar to the WRITE clock on a 3850. I force in DCI $0000 to reset the data counter, then LM over and over to load the next memory contents.

One of the data sheets I've read said that there's a fuse on the test pin that can be blown by connecting it to -7V. If so, the bits can still be extracted visually after decapping the chip. Here's a pic of a 3851's ROM array showing how the bits are arranged: http://www.seanriddle.com/psu.html I've decapped a 3870, but haven't posted pictures of it.

There are a couple of 3870-based chess computers that I dumped which are emulated in MESS.

http://www.seanriddle.com/f8.html

http://pdf.datasheetcatalog.com/datashe ... 295_DS.pdf

[BigEd]

Nice writeup and site Sean! (You will probably have seen Ken Shirriff's work at http://righto.com/ti and nearby.)