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EPROMr R2.1 EPROM Burner Assembly Instructions (Parallel Version)

Once you have completed the assembly directions on this page, you will have a burner that can be controlled directly by any DOS-based PC. MacOS, UNIX, Windows NT and other users should build the EPROMr 3 instead.

There is a FAQ (Frequently Asked Questions) page regarding this product. If you are having problems building or using the EPROMr, or if you require read/burn support for devices which aren't on the compatibility list, please consult this page.

The EPROMr burner is not really that complicated - it just has a lot of wiring which is difficult to illustrate neatly. I spent about two hours playing about with a draw package before I realized that it would be much simpler just to describe the wiring, rather than attempting to draw it. The scanned diagrams illustrate just how complicated it LOOKS. I make no apologies for the hasty diagrams - this is a prototype of an intermediate release of a hobbyist-grade product. Here is the schematic:

Parts Manifest
Qty	Item
2	4040 12-bit binary up counter
1	BC547 or equivalent NPN Si transistor (SS8050 is a substitute)
1	BC557 or equivalent PNP Si transistor (SS8550 is a substitute)
1	LM317 adjustable voltage regulator
1	7805 +5V regulator
1	470uF 25V electrolytic capacitor
1	10k trimpot
1	240R 1% metal-film resistor
10	33k 5% carbon resistor
1	82K 5% carbon resistor
1	8-way DIP switch
1	32-pin DIP IC socket (if you can't get a 32, cut down a 40). ZIF is recommended but very costly. Don't try to cut down a ZIF socket!
1	male 25-pin D connector
-	Veroboard, hookup wire, duct tape, etc.

Before you do anything else, grab the software for this unit (The archive also contains this file and the schematic diagrams, so if you prefer, you can look at all this information offline. The archive was compressed with WinZip, since it contains long file names).

The first functional unit we'll discuss is the power supply section. The EPROMr is designed to be powered from a DC plugpack with an output voltage of 14-20V. The prototype is powered off a multi-voltage unregulated DC plugpack set to 12V (since the plugpack is unregulated, its output under the tiny load of the EPROMr is around 14.2V). There are two voltages required by the circuit - +5V to power the counters and the EPROM itself, and +12.5V for the programming voltage. +12.5V is generated by IC1, an LM317 adjustable voltage regulator IC, in conjunction with R1 (240 ohm) and VR1 (10K). It's best to use a multi-turn trimpot for VR1, because the operative range of this control is quite small. Having said that, as you can see from the photgraphs on the main page, I personally used a regular carbon trimpot.

The +5V is derived from the +Ve rail using a 7805 three-terminal regulator.

Now it's time to build the meaty part which actually does the reading and writing. Refer to the schematic. Don't panic! The circuit is really very simple.

Let's start with the Vpp switching circuit. This consists of a pair of transistors (Q1 and Q2) and a couple of resistors (R10, 33K and R11, 82K).

Now for the address/control logic. In this circuit, the addressing and some control signals are generated by two cascaded 4040 12-bit binary up counters. Here's the pinout for the 4040:

	Pin	Pin
Q12	1	16	Vcc
Q6	2	15	Q11
Q5	3	14	Q10
Q7	4	13	Q8
Q4	5	12	Q9
Q3	6	11	Reset
Q2	7	10	Clock
Vss	8	9	Q1

The two 4040s are designated IC3 and IC4. IC3 is the "low" counter (it generates address lines A0 thru A11) and IC4 is the "high" counter (used to generate A12-A18 and control signals).

Start building the addressing circuit by soldering the 32-pin socket and the two 4040s onto the Veroboard - leave at least three holes between them. If you don't trust yourself not to overheat them, then use sockets. Put some kind of mark on the board to remind yourself which counter is high and which is low.

Now wire Q1 through Q12 from the low counter to address lines A0 through A11 on the EPROM, respectively. Q1 through Q3 on the high counter go to A12, A13 and A14 on the EPROM. The other lines go through various switches because the pin functions are different on different ICs.

Finally, add the parallel port connector. You'll note that the design specifies eight 33K pulldown resistors, R2-R9, across the eight data buss lines. These resistors are required to cope with the vagaries of some parallel ports - however, they will cause problems programming certain brands of EPROM (notably, Texas Instruments TMS27C256, vintage 1988). If you have problems, try connecting the common line to +5V rather than ground. If you plan to use this project exclusively with the serial interface, save yourself some grief and omit R2-R9 altogether.

Congratulations! You have now built the EPROMr hardware, and all that remains is to calibrate and test it. Connect the power supply, and attach the EPROMr to your PC's parallel port. Switch to the directory containing the EPROMr software, and run EPROM -d. The diagnostic mode will allow you to verify that all the control signals are working correctly, and will also allow you to adjust VR1 so that exactly 12.5V is supplied to the Vpp pin(s) of the device socket. For more information on the software functions, refer to the EPROMr control software documentation.

Attention: The only time when it is safe to have a chip in the device is when the EPROMr software is prompting you to insert a chip. If you leave the chip inserted while your PC boots or while Windows starts or exits, you run a risk of accidentally applying a programming pulse which may destroy data.