EPROM Programmer

Posted on Jul 2, 2012

The four 1K resistors on the output of U6 are too high in value for some parallel ports. Change these to 100ohm. Some LSI based parallel ports use active pull-up resistors and these are lower than the nominal 4K7 which causes a voltage divider effect. A bad design mistake. The eight LED dropper resistors are too low in value and cause pikes on the power rails which can effect the rest of the circuit. Change these resistors to 1K or greater. Another bad design mistake.

There is a new modification in the Jan 2000 issue of EA that describes a hardware modification to support EPROM's up to 1Mb. Whilst my software can cater for sizes up to 16Mb, I have no idea if this hardware modification is compatible with my software, and I have no plans to try it myself or even look into it conceptually, nor update my software to support it. In my humble opinion the whole design is WAY past it's used-by date (even was back when it was published) and needs a complete redesign, not just some ad-hock upgrade to an already unreliable design.

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