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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 25th May 2017, 8:25 pm   #1
SiriusHardware
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Default Motorola MCM68766C EPROM data?

Just trying to help out someone who needs one of these programming - the device list on my normally dependable Hi-Lo systems All07A programmer includes the MCM68764 and MCM68766... but not with the 'C' suffix.

Going from experience, any EPROM device with a 'C' anywhere in the part number usually needs a different programming voltage (VPP) and possibly / probably a different programming algorithm.

My net searches so far have turned up a datasheet which may well be for the 'C' variant, but most of it - including the critical line about VPP - is in Chinese. Another purporting to be for the MCM68766C turned out to be for the 'plain' MCM68766 device.

It can't be directly substituted with a 'common' 8K EPROM (ie, 2764 / 27C64) because it is a 'reduced pin count' device - an 8K * 8 EPROM in a 24-pin package.

Does anyone have a Motorola memory device databook sitting on the shelf, please?
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Old 26th May 2017, 11:59 am   #2
JacKam_
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Default Re: Motorola MCM68766C EPROM data?

Hi, I guess it is MCM68766 in ceramic package. I have pdf in English.

Thanks,

Jacek
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Old 26th May 2017, 12:43 pm   #3
Oldtestgear
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Default Re: Motorola MCM68766C EPROM data?

The "C" suffix is for the ceramic package according to the Motorola data book I found on the Bitsavers site. There is also a Cypress equivalent but that is even harder to find. It is a MOS device.

This was the EPROM variant of several custom ROM chips available back in the day. Many of the original ROMs fitted in test equipment are now failing & these are the only option without redesigning PCBs or making adaptors.

Hope this helps.

Phil
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Old 26th May 2017, 3:07 pm   #4
SiriusHardware
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Default Re: Motorola MCM68766C EPROM data?

Thanks both, this and other pointers suggest it should be safe for me to try to programme this device. The original - presumably a PROM - is actually from a NASCOM 2.
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Old 26th Jun 2017, 12:34 am   #5
SiriusHardware
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Default Re: Motorola MCM68766C EPROM data?

Quick update on this, your advice was correct and the MCM68766C programmed just fine with the basic device type Motorola / 68766 selected.

One for me to remember in the future.
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