Full Featured PC-Based 4Mbit EPROM Programmer
by David L. Jones

The PC controlled EPROM programmer described in the September/October 1993
editions of Electronics Australia by Glenn Pure has generated quite a deal of
interest, with many hundreds of kits being sold. Not very surprising
considering that you could build your own EPROM programmer for a little over
$100 !. The follow up article in November 94 describing enhanced software
drivers for the kit also proved extremely popular, with most constructors
opting for the improved software over the original BASIC source code. 

Being one the authors of the enhanced software drivers mentioned, I've
received many requests for an improved project that would support larger
device sizes, as the original unit could only support up to 256Kbit EPROM's
as standard. 

Many constructors asked for 512Kbit support, which was a relatively simple
hardware modification, but required new software to match, and many others
felt there was a need for a low cost programmer to support the newer 32 pin
EPROM's which are becoming very popular. In some cases cheaper than the 28
pin devices !. 

While it is possible to add support for larger devices on to the existing
design, it starts to become quite messy once you go to 32 pin 1Mbit EPROM's
and beyond. In fact, adding 32 pin EPROM support would require a new front
panel PCB and complete rewiring !. This would also require three separate
sockets to support the full range of devices. 

I therefore decided that it would be much better to redo the design from
scratch, and not only add support for 32 pin EPROM's, but also add other
bell's and whistles found only on the more expensive commercial programmers. 

My goal was to design a unit not much more expensive than the previous
design, yet add new features like full software control, device ID detection,
and support for 64Kbit to 4Mbit EPROM's.  I also wanted to make the project
easier to build by keeping the entire design on one single sided PCB without
wiring, thus eliminating the extensive wiring required by the previous design
which many constructors had problems with. The design would also operate off
the PC's parallel port like the earlier unit. 

I'm glad to say that the design to be described here meets all of these
goals, and delivers a project that can match much more complex commercial
units costing many times the price. A commercial programmer with the same
functionality will cost upwards of $350 !. 

The hardware design described here supports 2764, 27128, 27256, and 27512 28
pin EPROM's, 27010, 27020, and 27040 32 pin EPROM's, as well as certain types
of 64Kbit and higher EEPROM devices. All compatible variations on these
generic types are also supported.

DESIGN CONSIDERATIONS :
=======================

The first decision I made when redesigning the unit was to forego software
compatibility with the existing design. I didn't have much choice in this, as
the previous interface design could not be expanded to meet the new
requirements. There were also some limitations of the previous interface that
I wanted to overcome. What this means is that the existing software is not
compatible, even if they did support larger device sizes. 

The next task was to try and design the circuit to fit on one single sided
PCB. However, I quickly realised that a design using garden variety 74xx
IC's, while certainly possible, could not be easily fitted onto a single
sided PCB (no matter how much hair I lost trying !). 

Not willing to give up my single sided PCB quest that easily, I decided the
only way was to use a custom programmed LSI device. The result of which is
evident in the schematic. The single LSI device (a Lattice ispLSI 2032) does
virtually everything, except for the address counting (I ran out of pins for
that one !). 

The Lattice ispLSI 2032 device is an In-System Programmable (isp) Large Scale
programmable logic device. It contains the equivalent of over a 1000 standard
PLD gates, and can be completely programmed while in circuit. However, the
in-circuit programming feature is not utilised in this design. 

The circuit for the 2032 device is the equivalent of about 8 standard 74xx
series devices. Which is quite a saving in PCB complexity when you eliminate
a good number of 8 bit buses from running all over the board !. 

I also decided to drop support for the 24 pin 2716 and 2732 EPROM's supported
previously. Not only would it have overly complicated the design to add this
feature, but these EPROM's are no longer manufactured or included in most
data books !. This is the trend with commercial programmers as well, with
very few having support for the old 24 pin EPROM's. 

CIRCUIT DESCRIPTION :
=====================

As can be seen from the schematic, IC1 (the LSI 2032) handles all of the PC
parallel port interfacing, complete control of the address counter (IC's 2
and 3) and the switching relays. In short, it does everything !. The only
device not controlled by IC1 is relay RLY2, which is directly operated from
the parallel port. Why is relay RLY2 so special ? I hear you ask. Well, it's
not really special, it's just that I ran out of pins on IC1 !. 

IC1 connect's directly onto the data bus of the test socket (SK1), and is able
to read and write data to the EPROM under software control. The same goes for
address counter incrementing and resetting. IC1 also has programmable internal
pull up resistors which are used on selected pins (saving more PCB space !).

Due to the accommodation of the different EPROM sizes from 64kbit to 4Mbit,
and support for 28 and 32 pin EPROM's, some the pins on the test socket have
to perform more than one function. Pin's 22, 29, and 31 on the test socket
have to be switched between two different digital signals, which is done
internally to IC1 under software control. 

Pin's 3, 24, 26, and 30 are different in that they must be switched between a
power rail (Vcc or +12V Vpp) and a digital logic signal. This cannot be
accomplished directly by IC1, and must be done using the SPDT relays
RLY1/3/4/5. The relays are switched under software control through IC1 by
driving transistors Q1, Q2, Q3, and Q5, which in turn activate the
corresponding relays. 

The PCB design can accommodate two different relay footprints of two
different voltage ratings (6V or 12V). 

The two transistor circuit formed by Q6 and Q7 is used to switch the +12.5V
Vpp programming voltage on and off. Q6 is driven under software control by
IC1, which turns Q7 off and on via R8. R9 is used to hold Q7 off when Q6 is
not on, and similarly for R10 which holds the Vpp rail low when Q7 is not on.

The address counter used to supply the EPROM address, is generated by IC2 and
IC3. They are 12 bit binary ripple counters, with IC3 clocked directly from
IC1, and IC2 being clocked from the MSB Q12 output of IC3. Although the two
counters can form an address up to 24 bits wide, only 19 bits are used to
form a range up to 512K. The 512K address range will handle EPROM's up to
4Mbit (512K x 8) in size.

Support for 28 and 32 pin EPROM's in the one socket requires switching the
Vcc voltage to pin 30 (pin 28 on the 28 pin device), and is performed by
relay RLY5. 

A single PCB mounted LED, LED1 is used to indicate the presence of Vcc power
to the test socket. Make sure it is turned off before inserting or removing
an EPROM !. 

Relay RLY2 is used to switch the Vcc voltage to both the 28 and 32 pin
devices off and on. This allows safe insertion and removal of the EPROM to
and from the test socket, without having to manually switch off the power.

Relay's RLY1, RLY3, and RLY4 are used to switch the Vpp voltage onto the
required pins depending on which EPROM type is being programmed. Switching
Vpp onto the EPROM's A9 line (pin 26), was not done in the previous design,
and is used to enable an EPROM's identification code to be read.

Regulator REG2 is used to supply the Vpp programming voltage, with the
variable resistor VR1 used to set this voltage, which is usually within
12-13V. It also supplies the input to the other regulators. 

Regulator REG3 supplies the Vcc voltage to the EPROM. This is selectable
between 5V and 6V by the circuit formed by Q8. Q8 is driven by IC1 (again
under software control), and when turned on, parallels R12 across R11 which
produces a regulator output voltage of 5V. If Q8 is off, then only R11 is in
circuit which will raise the regulator output to the required 6V. REG3 is
also used to supply the coil voltage for the relays, which means that it will
carry a few hundred milliamps whilst dropping 6 or so volts. I've found that
the bolt used to secure REG3 to the PCB act's as a sufficient heatsink in most
cases, however a proper heatsink may be required.

REG3 is a simple 7805 5V voltage regulator which supplies the logic devices
IC1, IC2, and IC3. REG3 may require a small clip-on heatsink if it gets
overly hot, but will generally not require one. 

Although REG2 supplies everything on the board, including the other
regulators, it should not require a heatsink because it is only dropping a
few volts. The bolt used to secure REG2 to the PCB should be a sufficient
heatsink. But if the input to the regulator is more than 16V DC, REG2 may
require a small heatsink.

The circuit requires a 16V DC or 12V AC plugpack rated at 500mA or greater.
This input is full-wave rectified by diode bridge BR1, and filtered by C1. 

Without going into the details of IC1 and EPROM programming algorithms,
that's all there is to the circuit operation, as almost everything is under
complete software control. 

CONSTRUCTION :
==============

The project has been designed to accommodate everything including the test
socket and parallel port D connector onto the one single sided PCB. 
Construction is as simple as mounting the components onto the PCB, there is
no wiring to be performed. You should have little trouble following the
component overlay and circuit diagram, and experienced constructors will no
doubt jump straight in without reading the "how to" !. 

Start off with the 28 wire links, some of which are very close to the IC
sockets and will be difficult to neatly insert later. At this stage, the
voltage selection for the relays must be done. This involves installing one
of two different wire links. These links are marked with "6V" and "12V"
respectively on the component overlay. If you have relays with a 6V coil,
then install the "6V" wire link while leaving out the "12V" link, and
vice-versa if you have 12V relays. The coil voltage rating should be marked
on the relay case. 

Next install all of the resistors and IC sockets. IC1 requires a 44 way PLCC
(Plastic Leaded Chip Carrier) socket, which will require careful insertion to
avoid bent leads. Ensure that all of the leads are straight before inserting
this socket, otherwise it will require a lot of patience to align the pins to
the holes!. Also be sure to align the notch on the socket to correspond to
that shown on the component overlay, as the IC can only be inserted one way. 
The notch is at the bottom left hand corner of the PCB. 

IC2 and IC3 do not require sockets, however this will aid in servicing and
power up tests. If you are only going to use a 32 pin machine pin IC socket
for SK1, then this should be inserted now, otherwise if you have a ZIF (Zero
Insertion Force) socket this should be left until last. Leave the IC's out of
their sockets for now.

Now install the other components, ensuring correct orientation and placement
of polarised components. When installing the regulators, bend the leads over
and lay the regulator flat on the PCB to avoid breakage. REG2 and REG3 should
be bolted to the PCB with suitable bolts. 

The programmer is not housed in a case, but instead sits open on stick-on
rubber feet attached to the bottom corners of the PCB. This seems to be the
trend with a lot of commercial programming units, and does make good
economical sense. Why pay for the cost of a case if the design is completely
self contained on one PCB ?. However, there is nothing to stop you from
mounting it in a case if desired. 

SETTING UP
==========

The only adjustment that has to be performed prior to use, is that of the Vpp
programming voltage set with VR1.

But first, the power up checks must be performed. Start by applying power to
the board and measuring the voltage at the output of REG2. Adjust VR1 so the
output is set at 12.5V. If you can't get this voltage, then check the input
voltage, it should be at least 15V.

Now measure the output voltages of REG1 and REG3. They should be at 5V and
6V respectively. It would also pay to check the voltage at the power pins of
the IC's, which should be at 5V.

Turn the power off and insert the IC's, being careful to watch the
orientation. IC1 will only go into the socket one way, so don't try and force
it in. The bevelled corner on the chip should be positioned at the lower left
of the socket. 

Restore power to the board, and once again check the voltages on the IC's and
the outputs of the regulators. The output of REG3 may have dropped to 5V
depending on the power-up state of IC1, which controls the output voltage.

You can now connect the board to the PC's parallel port with a 25 way IDC
ribbon cable. This cable will require a female D25 on the programmer end, and
a male D25 on the PC end.

Now run the PCEBTEST program supplied with the software and follow the on
screen prompts to test out the rest of the programmer.

The programmer requires a DC supply of at least 2V above the required Vpp
voltage, which will usually work out to at least 15V DC. Some 12V AC
plugpacks may not be suitable for this project, due to the tolerance of the
plugpack voltage and mains input. In this case, use another type of plugpack
or drop the Vpp voltage down to the minimum required for the EPROM being
programmed. 

USING THE PROGRAMMER
====================

Documentation is supplied with the software on disk, so we will only discuss
the basic operation of the programmer here.

The program is an enhanced version of my software which I supplied for the
previous programer design (see EA Nov.94), although with extra features to
support the new programmer design. Note, this new version is NOT backward
compatible with the previous design. 

While the program supports all devices up to 4Mbit in size, this will require
around 600KB of free base memory. If you have less than this, then the
program will only support devices up to 2Mbit in size.

Apart from the memory requirement, the program is less than 50KB in size and
can be operated from a single floppy drive if required. No swap file is
required as on the previous version. The program is entirely text based and
does not require a graphics card to operate.

All three standard parallel port addresses are supported, and can be chosen
from the main menu. You only have to select the required port once, as it is
saved in the programs configuration file.

The screen interface and program operation is very similar to the previous
version, with single 'hot-keys' used to access all functions from the main
menu. The following basic functions are supported by the software :

Read
Program
Verify
Compare
Blank Check
AutoProgram
Device Detection
Load/Save/Edit data
CRC Checksum

The program is based around a central data buffer, which is used to hold the
data to be programmed or edited. Reading an EPROM's contents will place the
data in this buffer. The buffer contents can be loaded and saved to a
specified file on disk. The data can be viewed and edited in both Hexadecimal
and ASCII formats. 

The programmer does not have an ON/OFF switch, so an EPROM should only be
inserted or removed when the program is running at the Main Menu, with the
correct parallel port chosen. The program will disable all power and signals
to the test socket when at the Main Menu. Power will only be applied to the
socket when the user selects one of the commands that accesses the EPROM, at
which point LED1 will be ON. Do not insert or remove an EPROM while the LED
is ON !. 

When inserting a 28 pin device into the test socket, be sure to insert the
chip closest to the bottom of the socket. IE. the ground pin is common to
both 28 and 32 pin chips. Inserting the chip in any other position will not
work and possibly damage the device. 

The program supports a multitude of different device types, which can be
selected from within the Type library. The user is also able to add their own
device types to the library. The correct device type must be selected in
order for the program to communicate properly with the EPROM. 

Automatic device ID detection is a feature which enables the software to
automatically detect the brand and type of an EPROM. This is useful when the
markings on a device are hard to read. If device ID is enabled from the main
menu, then the program will try to detect the EPROM type before Reading,
Comparing, or Programming, and then automatically choose the correct device
type in the software. This is assuming that the ID of the EPROM (if it has one)
matches one that is already stored in the programs Type library.

Start and End addresses can be chosen to enable the software to only operate
on one part of an EPROM if desired. Checksum calculation is also scaleable to
the range between the specified Start and End addresses.

All of the timing for project, including the programming pulses, are
generated by the software. The software will calibrate itself when started,
which will take three seconds. If your PC has a turbo switch, then do not
touch this after the program has loaded, otherwise the timing routines will
be affected. 

Whilst the nominal programming voltage of 12.5V that was set during the
setup process should be adequate for the majority of EPROM's available, some
devices are more sensitive and may require adjusting the programming voltage.

Be sure to select the correct device type and algorithm before accessing an
EPROM. If in doubt, consult the relevant manufacturers data sheet. I've found
that EPROM's are quite easy to damage by using an incorrect algorithm and/or
programming voltage. In many cases the chip is not completely ruined, and
appears to function and program correctly except for occasional errors. This
was very frustrating when developing the project, as it was difficult to know
if it was a faulty chip, or the software !. 

One last safety message !. When erasing EPROM's, be sure to avoid exposure to
the Ultra Violet light used for this purpose. The high levels of UV light
used for EPROM erasing can permanently damage the eye's and skin. It is
recommended that only a good quality commercial eraser be used, to avoid
accidental exposure to UV light. 

In short, both the programmer hardware and software operate very similar to
commercial programmers, as well as providing most of their functions. I hope
you'll find the programmer easy to use and very functional.

Happy burning !.