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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 8th Nov 2022, 10:36 pm   #21
Pernod70
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Default Re: DM8678 replacement

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Originally Posted by Realtime View Post
As far as I know you canít directly read the character Rom in the DM8678, as thereís no data bus.
Correct, but you may have had it decapped.
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Old 11th Nov 2022, 9:09 am   #22
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Default Re: DM8678 replacement

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Originally Posted by Pernod70 View Post
Quote:
Originally Posted by Realtime View Post
As far as I know you canít directly read the character Rom in the DM8678, as thereís no data bus.
Correct, but you may have had it decapped.


Here are the font tables in an asm listing
Attached Files
File Type: txt FONT1 CAB,ZX80,Spectrum,CAH.asm.txt (20.9 KB, 13 views)
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Old 11th Nov 2022, 5:52 pm   #23
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Default Re: DM8678 replacement

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.
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Old 13th Nov 2022, 6:48 pm   #24
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Default Re: DM8678 replacement

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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?
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Old 13th Nov 2022, 7:57 pm   #25
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Default Re: DM8678 replacement

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Quote:
Originally Posted by Mark1960 View Post
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?
Iíll 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.
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Old 16th Nov 2022, 9:47 pm   #26
Realtime
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Default Re: DM8678 replacement

From what Iíve read the Microtan had sockets for both the BWF upper case and CAE lower case character generators. I donít suppose the silk screen on the CRC version you have is poorly printed and itís actually CAE?
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Old 16th Nov 2022, 10:29 pm   #27
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Default Re: DM8678 replacement

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 wonít know until I try it. Iíd 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.
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Old 26th Nov 2022, 10:37 am   #28
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Default Re: DM8678 replacement

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/
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Old 27th Nov 2022, 5:04 pm   #29
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Default Re: DM8678 replacement

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Originally Posted by Realtime View Post
From what Iíve read the Microtan had sockets for both the BWF upper case and CAE lower case character generators. I donít suppose the silk screen on the CRC version you have is poorly printed and itís 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.
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Old 28th Nov 2022, 4:46 pm   #30
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Default Re: DM8678 replacement

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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.
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Name:	DM8678CAB.jpg
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File Type: zip FONT1 CAB.zip (408 Bytes, 7 views)
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Old 2nd Dec 2022, 9:45 pm   #31
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Default Re: DM8678 replacement

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