Do you think you might be able to program the 12v 27C' series EPROM's which require switchable 5.0v & 6.25v on VCC and switchable 5.0v & 12.5v on VPP?
I built a programmer long ago for the 12v 27C' EEPROM's that connected to my Pete Dunster 68HC11F1 board. It could also program 28C' series EEPROM's.
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The 12v 27C' devices are quite popular and readily available (new and surplus). I still have a stash of shiny 'new old stock' 27C' series EPROM's and I considered a new Flash programmer design with the option of adding a pair of 50¢ MT3608 'boost' modules to provide the switchable VCC and VPP voltages since the 'enable' pin on these modules will place either the boost voltage or the 5v input voltage onto the output. It does however require a wee bit of surgery on the modules to expose the 'enable' pin.
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For 5v EEPROM, Flash ROM, and nvRAM devices I use an Uno and a programmer shield combo' that costs about $6, including the $3 Uno clone with mini or micro usb connector.
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