Date   : Fri, 30 Mar 2001 00:30:01 -0800
From   : Angus Duggan <angus@...>
Subject: Re: BBC Micro EPROM Programmer

Chris Richardson writes:
>Hi Angus
>I would appreciate photos for the website if you can dig it out...

I just took some photos, and have discovered that the board diagram that I
found doesn't quite match what I implemented...I'll have to reconstruct the
circuit diagram and see if it's feasible. The photos show a complete mess of
wires, I don't think they'll be much use without a circuit diagram. It looks
like I used a couple of 8-way latches to set the address lines, some form of
multiplexing on CB1/CB2 off the user port VIA control lines to select which
latch or the data bus is active, and an inductor circuit pinched from the
Beebug programmer for the programming voltage.

On the topic of the Beebug programmer, I have an errata sheet which I believe
is a correction to the correction scanned by Colin. I may try to scan it
after the weekend.

For those who want to get a head start getting parts, you will need (note the
striking resemblence to the Beebug list):

* 20 way ribbon cable (pity I'm not back in the UK, I picked up about 20m of
  this for free a while back, and have plenty left :-)
* 1 of 20 way dual in line IDC socket
* 2 of 74374 latches
* 1 of 28 way DIL ZIF socket (or be a cheapskate like me and use a normal
  socket, but be *very* careful getting EPROMs into/out of it.
* 2 of 10 mH open wound choke
* 2 of 1.2 kOhm resistor (all resistors 4W)
* 3 of 4.7 kOhm resistor
* 1 of 20 kOhm resistor
* 1 of 330pF capacitor
* 1 of 47uF, 63v capacitor
* 1 of TL497A DC-DC converter
* 1 of 74LS08
* 1 of 74LS74
* 1 of 74LS00
* 1 of dual-pole changeover microswitch (6 connections)
* vero-board (I fitted it in a 37 x 37 hole (3.7" x 3.7") board, but the
  wiring is very ugly to do that.

I'll have to check if it feasible to adapt it for 27256 EPROMs, or at least
add a select switch for the high address line; last time I tried to bug
27128s, I couldn't find any.

On the subject or EPROM programming, does anyone know of a cheap way of
rigging up a UV eraser? I found a bug in my DFS (needs a one-byte change) a
bit back, and I want to re-blow the ROM.

a.