mirror of
https://github.com/TomNisbet/TommyPROM.git
synced 2024-11-28 18:51:39 +00:00
27 lines
1.2 KiB
Markdown
27 lines
1.2 KiB
Markdown
---
|
|
title: "8755A Hardware Design"
|
|
permalink: /docs/8755A-hardware
|
|
exerpt: "TommyPROM Arduino programmer for the Intel 8755A"
|
|
---
|
|
|
|
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.
|
|
|
|
The Intel 8355 is a one-time programmable version of the 8755A. This design can be used
|
|
to read the 8355.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
[](images/TommyPROM-8755A-sch.png)
|
|
|
|
Eagle-format schematics can be downloaded from the
|
|
[hardware project page](https://github.com/TomNisbet/TommyPROM/tree/master/hardware).
|