DM8678 replacement

[Pernod70]

Originally Posted by Realtime

As far as I know you can’t directly read the character Rom in the DM8678, as there’s no data bus.

Correct, but you may have had it decapped.

[Realtime]

Originally Posted by Pernod70

Correct, but you may have had it decapped.

Here are the font tables in an asm listing

[Realtime]

The Tech Notes for the RealView VDU card and DM8678 Emulator modules are available here. It's aimed at giving enough info to understand the operation of the cards and perhaps make modifications (at your own risk ). It's not a resistor-by-resistor description, but if you need any clarifications then let me know.

[Realtime]

Originally Posted by Mark1960

Does anyone know what character set is in the 86S64CRC variant?

The closest reference I found was CRH, but no description of what font that has. I wonder if it is a custom font? Nat Semi DM8678 data sheet describes how to submit a font on punched cards. Have you been able to test the device?

[Mark1960]

Originally Posted by Realtime

The closest reference I found was CRH, but no description of what font that has. I wonder if it is a custom font? Nat Semi DM8678 data sheet describes how to submit a font on punched cards. Have you been able to test the device?

I’ll need to set up my Microtan 65 and see if it still works. I ordered the CRC variant at the same time as the BWF version that I ordered for my second Microtan main board, this one never had a character generator, it was set up to play space invaders. I was hoping the CRC might be a lower case variant. I also have a couple of 86S128CQH as a backup plan for lower case on the Microtan as I never had the lower case option character generator.

[Realtime]

From what I’ve read the Microtan had sockets for both the BWF upper case and CAE lower case character generators. I don’t suppose the silk screen on the CRC version you have is poorly printed and it’s actually CAE?

[Mark1960]

Yes the microtan has two sockets for character generators, mine has both sockets fitted but I only had the upper case generator. The CRC might be a lower case variant, I guess I won’t know until I try it. I’d prefer not to do a wire mod to use the 86S128, though I have another main board that I might mod. The other board is not in good condition, all ICs were in sockets but most have been robbed, it was also modded to fit 4k ram as a stack of 2114s and is coated in brown dust that I suspect is from cleaning rust off a car in the garage. The best of the two boards has amost all ICs soldered to the board, I keep putting off trying to apply power to see if it still works.

[microtan_man]

According to their datasheet (www.microtan.ukpc.net/Datasheets/DM8678.pdf) National Semiconductors didn't make a DM8678 CRC variant.

If looking for replacements for the Microtan, a piggy-back module has been developed here: http://microtan.thegrahamfamily.me.u...r-replacement/

[ortek_service]

Originally Posted by Realtime

From what I’ve read the Microtan had sockets for both the BWF upper case and CAE lower case character generators. I don’t suppose the silk screen on the CRC version you have is poorly printed and it’s actually CAE?

Maybe it was actually CAB? - As a Bywood Electronics advert at the time said:
DMB67B Char Gen ....... . . £15.20 (both CAB & BWF avail.)

- See attached page extract / the full magazine can be found at:
https://worldradiohistory.com/UK/Per...No.1-S-OCR.pdf

Rather expensive (even before 8%? VAT back then), and I wonder how much NS blank PROM's were around that time, being as they gave you the contents to generate your own Character PROM's.

[Pernod70]

Originally Posted by Realtime

The fonts were coded by hand from the DM8678 data sheet (or application note) - I believe they are accurate.

As I'm now using your CAB font I noticed a few differences from the datasheet, notably the characters C, U, $, %, 3.

Attached the corrected binary.

[Realtime]

Thanks for posting the corrected font table. I had noticed the 3 was incorrect but not the others.