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Paul Berger (Canada) · 06-17-2020, 08:05 PM

(06-17-2020 03:33 PM)J-F Garnier Wrote:
(06-17-2020 02:51 PM)cmurillo Wrote: So... I take it from this that read accesses to the EPROM are slowed down by this mechanism, making this HHP device inherently slow?

Well, not necessarily. It may be, since the HALT signal is present in the card reader, but I don't think it is used by the 1LJ4 interface chip. You can have a look at this document summarizing the known information about this chip.
It may be the problem with CMOS parts that may need more time to properly power up.

BTW, if you find a way to use a 64K EPROM in the HHP EPROM carrier, I would be very interested !

J-F

Halt is not connected to anything on the HHC module that I have. Pin 1 which would be A15 on a 64K EPROM is connected to Vcc of the EPROM, in fact the trace from the collector of the transistors to pin 28 goes through pin 1. The transistors are connected in parallel and are PNP type with the emitters connected to +5V the bases connected to the -OE signal and the collectors to Vcc of the EPROM.

The module I have in front of me is the two jumper version which I suspect is functionally equivalent to the version with one 3 pin jumper. One pin of both 2 pin jumpers is connected to pin 27 of the EPROM. On the jumper adjacent to pin 1 the other pin goes to pin 9 of the 1LJ4 chip, on the jumper adjacent to pin 28 the other pin is connected to pin 28 so depending on which jumper is installed pin 27 is either connected to A14 or Vcc.

The big issue for determining if a 64K EPROM might be used is that we do not have the specs for the 1LJ4 chip, all the information in the document that Jean-Francois linked I determined by observing a few HHC modules. There are 3 pins that differ between a module with 4 X 8K memory devices and a device with a single 32K device, but all 3 are connected to Vdd when 8K devices are used and all 3 are connected to ground, who knows what other combinations of these pins would yield, it certainly is possible to have 64K and even 128K single ROM units, however at the time these modules where designed it does not appear that there was 64K EPROMs yet, Intel's 1984 memory data boot does not list any, and it is likely that the 1LJ4 chip was designed even earlier.