Microelectronics | 640K ROM Matrix

Synopsis

After playing around with the 32K ROM Matrix, my experiments with EPROM storage continued. This time, with larger EPROM ICs. I've obtained a few larger EPROMs from a dump of old 80286 and 80386 computers at the Technical University. There were so many of them, but I only picked a handful. Unfortunately, all that hardware was going to the recycling facility.

Schematic Diagram

Again, the schematic depicts a simple circuit, this time, based on larger capacity EPROMs and a 3:8 line decoder of type 74HC138.

Fig. 1: Electrical Principial Schematic

Fig. 2: Top Layer Printed Circuit Board

Fig. 3: Bottom Layer Printed Circuit Board

The LED driver circuit is borrowed (unchanged) from the 32K ROM Matrix design.

Construction and Pictures

This time, the PCB is single-layer. The top layer only has a few wire bridges.

This is the PCB before installing the sockets for the EPROM ICs.

The bottom-layer PCB looks like this.

Just a test. I don't (ever) plan to solder EPROM ICs to the PCB directly, without sockets.

The completed PCB assembly. The 3:8 decoder is not yet installed.

A top view of the PCB.

And the solder side. The PCB is also home-made, using the toner transfer method. Etching was done with ferric chloride (FeCl₃), and finally a layer of flux was applied to protect the copper traces.

As for possible uses for this circuit... I'll let your imagination go wild. I was just having fun learning digital electronics.

Thank you for reading this page, and I hope you found it useful.