Hand Held Products 71M/M eprom carrier question

[J-F Garnier]

(06-16-2020 06:51 PM)cmurillo Wrote:  Initially, I tried to use an NM27C256BQ thinking that the CMOS part would consume less power. The rom was successfully recognized, but as soon as I made heavy use of the matrix functions in it, a crash occurred and I got a "Memory Lost". I then programmed the same EPROM that came with the 71M/M (the said HN27256G) and this one has been working fine. I can only assume that the NM27C256BQ produces some spikes in the power supply that the HP-71B doesn't like.

I had the same issue when I was using the HHP EPROM carrier at the time.

The HHP was designed to manage NMOS EPROM, since the CMOS parts were just introduced on the market and still rare and expensive.
To keep the power consumption low, HHP switched the EPROM supply off when not used, and turned it on only for the duration of a read access.
Obviously, the CMOS parts don't accept this operating mode.

At the time, I wanted to use CMOS parts, and so I bypassed the switching element (a transistor), as you can see on attached picture, so the EPROM was always powered on and the problem was solved.

J-F