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--- | ||
title: "8755A Hardware Design" | ||
permalink: /docs/8755A-hardware | ||
exerpt: "TommyPROM Arduino programmer for the Intel 8755A" | ||
--- | ||
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A special version of the TommyPROM hardware was developed to support the Intel 8755A | ||
EPROM with IO chip. This is a 2Kx8 UV EPROM with additional I/O ports. | ||
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The Intel 8355 is a one-time programmable version of the 8755A. This design can be used | ||
to read the 8355. | ||
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The Intel 8755A uses a multiplexed data and address bus, plus 3 additional address lines. | ||
Most Arduino hardware has enough pins to support this directly, so no shift register | ||
hardware is needed for addressing. An Arduino pin is also used to drive the ALE latch pin. | ||
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The 8755A requires the Vdd pin to be be switched between 5V and 25V during the programming | ||
of each byte. A simple transistor circuit is used for this. No voltage regulator circuit | ||
is present here for the programming voltage. Because this is designed as a quickly | ||
assembled hardware design, a triple output bench supply was used to provide the 25.5V, | ||
5.5V and 5V outputs. | ||
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[](images/TommyPROM-8755A-sch.png) | ||
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Eagle-format schematics can be downloaded from the | ||
[hardware project page](https://github.com/TomNisbet/TommyPROM/tree/master/hardware). |