TommyPROM/docs/pcb.md

title	description	has_children	nav_order
Printed Circuit Board	TommyPROM Arduino 28C256 programmer PCB	false	35

Printed Circuit Board

Although it was originally designed as a one-off programmer to be used on a breadboard, there are now some PCB versions.

28C256 PCB

A PCB version for the 28C256 and 28C64 chips was built to support a SAP-1 TTL breadboard computer. This project required a lot of burns for its microcode and the PCB version with the ZIF socket was much quicker than prying the chips out of a breadboard without disturbing any of the wires.

The KiCad design files are in the project repo.

TommyPROM-32

A new PCB is in progress for 32-pin EEPROM and Flash chips. This design uses a set of headers that allow any of the signals to the target chip to be re-routed. The default configuration, with just jumper shunts installed, is wired for the SST39SF0x0 chips.

Many other chips, particularly if they follow JEDEC standards, can be supported by removing shunts and adding just a few jumper wires.

Chips with fewer pins can also be supported. There are power pins in place to support 28-pin and 24-pin chips with a shunt to the correct VCC pin.

Power inputs and a switch are provided to support older flash and EEPROM chips that need higher programming voltages. Many of these chips just need a higher voltage, like 12V, applied to the VPP pin continuously during the programing and verification cycle. In normal operation, the 5V VCC signal is also applied to the VPP pin. The board has VPP inputs for two voltages. Applying 12V to VPP In High and 5V to VPP In Low lets the VPP output be switched between these two voltages using a manual slide switch for programming.

For chips that require a high voltage VPP pulse during programming, some external switching circuitry will be needed to allow the Arduino to control the VPP voltage. There is a header connected to the unused D13 pin that can support this. See the Intel 8755 version of the hardware for an example of voltage switching by TommyPROM.