Here are a few Projects I have made for the SYM

EPROM Programmers:

It should be noted that the EPROM programmers listed below were developed as the need arose to have a particular chip programmer.  The they are listed roughly in the order that they were developed. 

All of the designs used a simple LM 723 voltage regulator circuit to supply the 21, 25 and 27 volts as required.  I built a separate LM723 circuit for each voltage required. This low current supply was built on the same supply that supplied the SYM +5 volts.  These can be seen in the photo of the power supply.   Each voltage was adjusted and available without the need to re-adjust anything.  Here is the design notes for the LM 723 circuit for the 2708 EPROM others are similar.

 The Universal board that is listed at the end could be modified to handle some of the earlier chips, but by the time I had evolved to build the Universal Programmer, I already had the earlier boards built and it would have been a waist of time to re-write the code for the earlier chips. 

If I were going to build a board to program the 2532 today for instance, I would build the Universal Programmer design rather than the 2716/2532 design, because the Universal can easily be adapted to many other chips.  The Universal Programmer can handle a 28 pin device or up to a 27256 or 32k chip.  A 16 pin DIP header "personality module" is plugged into the board to set up the signals for the various chip pin outs.  Modifying the design to accommodate a new chip is simply a matter of making a new header plug and modifying the SYM code to do the programming.

 2708                                      Programs 2708 Chips 

 2716/2532                            Programs 2716 and 2532 Chips

Universal Programmer             

One board that will handle a variety of chips.  A small jumper block  is plugged onto the board to select the type of chip to be used.  The following chips are currently supported.  Other chips may be easily programmed by making new personality jumper blocks and modifying the programmer program code.  Here are photos of the board.

To make a programmer for a different chip first study and update the EPROM pin-out chart.  Then markup the worksheet.  After marking up the worksheet, make a new header plug based on the worksheet (small circles are pins on the header plug-socket).  Then modify the source code for the closest chip size I have already done.  After studying the completed chips, it will be obvious the changes that need to be made.  All of the source code is pretty well documented.  Note again that the PB4 signal at the SYM connector Y has been buffered thru one of the SYM on board jumperable transistors.  This could be moved off of the SYM board if desired.  The SYM came with these buffer transistors in the circuit and I just used the SYM as it was wired.

2732           Drawing     Source Code    SYM object code

2764            Drawing    Source Code    object code

27128          Drawing    Source Code    

All of these programmers have been used extensively EXCEPT THE 27128 model.  This 27128 model has been built but I do not remember using it.  I would proceed with caution on this design.  It looks ok,  but I am watchful on any new design until it has a dozen or more uses.

Larger EPROM chips that exceed the my 32k RAM size could also be programmed by splitting the EPROM into sections and doing half at a time and so on.  The programming source code would not vary much.