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HHP-32k 41C ROM Emulator - Dip switches?
12-14-2017, 06:13 AM
Post: #13
RE: HHP-32k 41C ROM Emulator - Dip switches?
You talked to the Jim DeArras! Wow!

As you probably know, an HP-41 port occupy 8K, and early modules are either 4K or 8K. Initially there was a 4K chip and 8K was achieved by using two such chips (increasing the cost of a module).

Later HP introduced the 1LG9 (see chapter 11 of SDS-II manual). This is a a 12K chip that can be configured as 4K, 8K or 12K. So the same chip could be used to single, double and even a larger module (Advantage module). However, to avoid occupying more space than what is designated by a physical port, a bank switch scheme was introduced.

HP also used bank switching for the HP-41CX operating system and for the IR printer module.

Judging from the labels on the EPROMs they probably contain the firmware for the IR printer module (it is named Blinky).

I would guess that the B1 holder is bank 1 (main bank), B2 is the banked image and the smaller EPROM contains the upper bits for both pages. The printer firmware occupies page 6 (0110), so the DIP switch to the left could be the address as it shows that pattern.

This was very interesting, thank you for sharing!

Maybe you could read the contents of the EPROMs and compare with a known IR printer image, to see if that is the case and whether it contains an earlier version of the firmware?

I had a quick look at the patent and it basically seems to describe how early MLDLs like the one described in PPC CJ by Lynn Wilkins worked, by turning on EPROMs when accessed. Was that patent enforced and MLDL makers payed patent money? I based my own home made MLDL on that design, but I used a single 6164 (8K) EPROM for each 4K page and read out bits twice and even powered it up a cycle earlier as it was mentioned that the MLDL design would not work with a speeded up HP-41, and my HP-41 was running at 2x. It worked well and I got good mileage with that device for years.

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RE: HHP-32k 41C ROM Emulator - Dip switches? - hth - 12-14-2017 06:13 AM

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