An EPROM Programmer for 2716 and 2732

by A. Hall

This simple design using the Nascom PIO lets the microcomputer do all the work and reduces the hardware requirements to 2 4040 CMOS counter, a few small components, a piece of Veroboard and a 25 volt power supply. It gives you a ‘user-friendly’, almost foolproof design for just under 1K of object code which can either be stored on tape and operated from RAM or itself programmed into an EPROM for use. The software is written for Nas-Sys 1 and will run on a Nascom 2 or expanded Nascom 1.

The program sets the ports to mode 3, initiates the outputs, checks the 5 volt supply and reminds you to switch on but not insert the EPROM yet.

It asks whether a 2716 of 2732 is to be programmed, reminds you to set the type switch and checks that it is in the correct position.

It then tells you to switch off, insert the EPROM and switch on again and, after checking that the supply has been cut and restored, finally displays the menu of options, and of which may be selected. These are :–

1. Check EPROM completely erased.
2. Dump to RAM for examination.
3. Program and check against source.
4. Return to monitor.

Options 2 and 4 allow use of the normal tabulate function to find unused sections of the EPROM and option 3 programs as many bytes as required from any address in memory to any part of the EPROM.

When the RAM source address, EPROM start address and number of bytes have been entered, a prompt for a final start command is given to allow time to cross-check before committing the EPROM to programming.

During the latter, a pair of rapidly changing symbols is displayed to avoid the impression that nothing is happening. When both symbols are null characters, the programming is complete and the EPROM is checked against its RAM source and a correct or error message displayed before the program returns to the menu.

Port A is used to write data to or read it from the EPROM and Port B uses four bits as outputs to control the 4040 address counter, the programming logic and the voltage switch, and two bits as inputs to check the switch positions. The latter may