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27 lines
1.2 KiB
Markdown
27 lines
1.2 KiB
Markdown
---
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title: "8755A Hardware Design"
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permalink: /docs/8755A-hardware
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exerpt: "TommyPROM Arduino programmer for the Intel 8755A"
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---
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A special version of the TommyPROM hardware was developed to support the Intel 8755A
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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
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to read the 8355.
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The Intel 8755A uses a multiplexed data and address bus, plus 3 additional address lines.
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Most Arduino hardware has enough pins to support this directly, so no shift register
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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
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of each byte. A simple transistor circuit is used for this. No voltage regulator circuit
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is present here for the programming voltage. Because this is designed as a quickly
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assembled hardware design, a triple output bench supply was used to provide the 25.5V,
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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
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[hardware project page](https://github.com/TomNisbet/TommyPROM/tree/master/hardware).
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