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Testing
Connect the unit to a 5V and 12.6V supply. If a test meter is to hand, check for about +9V on pin 2 and -9V on pin 6 of IC1 (MAX232).

Connect the unit to the serial port on your PC, and run the program "SER-TEST.EXE" on the software disk. When prompted, type "1" or "2" followed by <Enter> to say which serial port you are using. The program does nothing more exciting than wait for you to enter a 2-digit hex number (followed by <Enter>) and then sends it to the programmer. It then attempts to read back a number, if it's successful it prints the number otherwise it prints "**". To exit just press <Enter> on it's own. All the responses in this section will be shown with quotes ("") around them - just type the number (followed by <Enter>), don't type the quotes.

Connect the programmer to your PC's serial port and a suitable power supply. Switch the programmer to 27512 and Read, and press Reset. Type "00" on the computer, and the software should respond with "FF". Whatever two digit hex number you type now should bring the response "FF", since the unit is reading the EPROM data lines, which with no EPROM will be pulled high by RN1.

We will now pull one of the data lines low, to give a different reading. Fit a piece of wire between pins 9 and 12 of the EPROM ZIF socket. If you type a number now the unit will return "FE". Leave one end of the wire in pin 12, and connect the other end in turn to pins 10, 11, 13, 14, 15, 16 and 17. Type a number in each case and you should get the following responses - "FD", "FB", "F7", "EF", "DF", "BF" and "7F" respectively. Remove the piece of wire, and switch the unit to Off. Now if you type a number the unit will not respond so the software will show "**".

Now switch the programmer to Program. Type "00", and "00" should be returned. Using a logic probe, test meter or oscilloscope, check the logic levels on pins 9, 10, 11, 13, 14, 15, 16 and 17. They should all be low.

Now type "01". The unit should return "01", and pin 9 should now be high, and the others should remain low. Now enter "02", "04", "08", "10", "20", "40" and "80" in turn. In each case the unit should return the number you entered. After each entry, check the logic levels on the data pins, only one should be high in each case - 10, 11, 13, 14, 15, 16 and respectively.

Switch the unit back to Read, and press Reset. Press Enter on it's own to quit the software then run "ADR-TEST.EXE", which is also on the disk. Since the address counters are incremented when a byte is sent, it would take a long time to get the count to 65535 manually! ADR-TEST does it automatically, and pauses at four points to allow you to check the logic levels. Follow the instructions on screen.

The expected logic levels on the address pins at the four pause points.

If these readings are OK, and the preceding tests were also successful you can be fairly confident that the unit is working correctly. The only sections that weren't checked were some of the device and mode switching. However the likelihood of problems here is remote if you were careful with the switch wiring.

If you have a blank EPROM and a suitable hex file available, you can try programming a device using the information given shortly.

The Case
The prototype was constructed in a plastic case, 190mm * 165mm * 68mm, see parts list for details. A suitable overlay for the front panel is shown in figure *. Two photocopies may be taken (enlarge to 162mm * 64mm), one can then be used as a drilling template while the other may fixed to the front panel with clear self-adhesive vinyl.

Cut a rectangular hole in the centre of the top for the ZIF socket, then mount the PCB on suitable spacers. The sockets for DC power input and RS232 input are fitted on the rear panel.