2022-11-25 03:57:01 +00:00
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---
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2022-11-25 13:25:49 +00:00
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title: Printed Circuit Board
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2022-11-25 03:57:01 +00:00
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description: "TommyPROM Arduino 28C256 programmer PCB"
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has_children: false
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nav_order: 35
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---
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# Printed Circuit Board
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Although it was originally designed as a one-off programmer to be used on a breadboard,
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there are now some PCB versions.
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## 28C256 PCB
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2022-11-25 13:25:49 +00:00
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A PCB version for the 28C256 and 28C64 chips was built to support a SAP-1 TTL breadboard
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computer. This project required a lot of burns for its microcode and the PCB version
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with the ZIF socket was much quicker than prying the chips out of a breadboard without
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disturbing any of the wires.
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2022-11-25 03:57:01 +00:00
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The [KiCad design files](https://github.com/TomNisbet/TommyPROM/tree/master/schematics)
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are in the project repo.
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[](images/TommyPROM-pcb.jpg)
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## TommyPROM-32
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A new PCB is in progress for 32-pin EEPROM and Flash chips. This design uses a set of
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headers that allow any of the signals to the target chip to be re-routed. The default
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configuration, with just jumper shunts installed, is wired for the SST39SF0x0 chips.
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2022-11-25 13:25:49 +00:00
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Many other chips, particularly if they follow JEDEC standards, can be supported by
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removing shunts and adding just a few jumper wires.
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2022-11-25 03:57:01 +00:00
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2022-11-25 13:25:49 +00:00
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Chips with fewer pins can also be supported. There are power pins in place to support
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28-pin and 24-pin chips with a shunt to the correct VCC pin.
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2022-11-25 13:25:49 +00:00
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Power inputs and a switch are provided to support older flash and EEPROM chips that need
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higher programming voltages. Many of these chips just need a higher voltage, like 12V,
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applied to the VPP pin continuously during the programing and verification cycle. In
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normal operation, the 5V VCC signal is also applied to the VPP pin. The board has VPP
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inputs for two voltages. Applying 12V to __VPP In High__ and 5V to __VPP In Low__ lets
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the VPP output be switched between these two voltages using a manual slide switch for
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programming.
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For chips that require a high voltage VPP pulse during programming, some external
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switching circuitry will be needed to allow the Arduino to control the VPP voltage. There
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is a header connected to the unused D13 pin that can support this. See the
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[Intel 8755 version of the hardware](hardware/#intel-8755a-hardware-version) for an
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example of voltage switching by TommyPROM.
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