Replica PROM Programmer Board

Replica PROM Programmer Board

Based on the Issue 1 schematic and photos.

The PROM Programmer Board has positions for fitting two ZIF sockets for the ICs being programmed.  This part of the board is removable so that it can be remotely connected or alternatively panel mounted sockets can be wired directly to the board (this is how Acorn intended as there are photos of the PROM Programmer with a 5HP wide front panel with the ZIF sockets fitted).

I chose not to do this as its difficult to wire directly to the ZIF sockets as their legs are short and so don't protrude through the panel.  3M Textool make receptacles for ZIF sockets, these are intended to be used so that the ZIF sockets can be replaced when worn out.  Usefully they have long legs that can easily span the gap from the front panel to a PCB mounted behind, unfortunately they're not easy to find and expensive (got mine from Mouser).  I have designed a small PCB that sits neatly behind a double width 10HP panel.

The PROM Programmer requires 12V and 26V for programming PROMs and EPROMs respectively, it is intended that these voltages are fed in via the backplane but I don't like the idea of having these hazardous (to TTL) voltages on the backplane having destroyed an expensive 6502 back in the early 80's !  I have designed a half depth Eurocard with a couple of low cost switch mode PCB modules on board to power the programmer. This extra PCB sits neatly in the unused backplane socket behind the double width panel.

PROM Programmer Power Supply

A note about the power supplies - the technical manual has a slightly ambiguous comment 'When programming EPROMs without the 12V supply IC5 should be removed', IC5 is the 4016.  If the programmer is always used with both the 12V and 26V supplies present then IC5 isolates the 8255 from the 12V programming signals on the data lines when programming a PROM.  The problem they are raising is that if you are programming EPROMs and only have the 26V supply present IC5 will not function as it is powered from the 12V supply.

A word of caution - R12 gets hot !

Schematic

Bill Of Materials

Front Panel Assembly

 

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