mirror of
https://github.com/TomNisbet/TommyPROM.git
synced 2024-11-22 10:31:39 +00:00
113 lines
6.3 KiB
Markdown
113 lines
6.3 KiB
Markdown
---
|
|
title: Hardware Design
|
|
description: "TommyPROM Arduino 28C256 programmer hardware design"
|
|
has_children: false
|
|
nav_order: 3
|
|
---
|
|
|
|
# Hardware Design
|
|
|
|
## Basic Hardware Version
|
|
|
|
The hardware uses an Arduino to write data and to toggle control lines with the
|
|
appropriate timing to access the PROM. A pair of 74LS164 serial to parallel shift
|
|
registers latch the address lines. Use of the shift registers allows the Arduino to
|
|
control up to 16 address lines using only 3 output ports. This design will read and
|
|
program the 28C series chips and can read most other parallel ROM chip families.
|
|
|
|
The basic circuit is as follows:
|
|
* Pins D2..D9 are wired to the data lines on the target PROM.
|
|
* Pins A0..A2 are wired to the WE, CE, and OE control lines on the target PROM.
|
|
* Pins A3..A5 control shift registers to produce the address lines.
|
|
* Pins D10..D12 control A16..A18 for chips larger than 64K bytes.
|
|
|
|
Note that the existing design uses 74LS164 shift registers, but another 8-bit parallel out
|
|
shift register, like the 74LS595, could be used instead with some pin changes.
|
|
|
|
When using the 74LS595 instead of the 74LS164, there is an additional output latch that
|
|
needs to be pulsed to put the contents of the shift register on the output lines. The
|
|
code supports this by uncommenting the _#define SHIFT_REGISTER_IS_595_ line in
|
|
Configure.h. The D13 line from the Arduino controls the RCLK latch on the '595. The table
|
|
below shows the connections when using either the 74LS164 or the 74LS595 for the address
|
|
shift registers. USR refers to the Upper Shift Register (A<sub>8</sub>..A<sub>15</sub>)
|
|
and LSR refers to the Lower Shift Register (A<sub>0</sub>..A<sub>7</sub>).
|
|
|
|
|Arduino |74LS164 |74LS595|
|
|
|:---: |:---: |:---: |
|
|
|A0 |ROM WE |ROM WE|
|
|
|A1 |ROM CE |ROM CE|
|
|
|A2 |ROM OE |ROM OE|
|
|
|A3 |USR CLK |USR SRCLK|
|
|
|A4 |LSR CLK |LSR SRCLK|
|
|
|A5<sup>1</sup> |LSR+USR A |LSR+USR SER|
|
|
|D2..D9 |ROM D<sub>0</sub>..D<sub>7</sub> |ROM D<sub>0</sub>..D<sub>7</sub> |
|
|
|D10..D12<sup>2</sup> |ROM A<sub>16</sub>..A<sub>18</sub>|ROM A<sub>16</sub>..A<sub>18</sub>|
|
|
|D13<sup>3</sup>|-- |LSR+USR RCLK|
|
|
|
|
Notes:
|
|
1. The data pin on A5 is connected to both the Upper Shift Register (USR) and the Lower Shift Register (LSR).
|
|
2. The upper address lines are not needed for 28C64 and 28C256 chips, but are used for
|
|
larger chips like the 27C040.
|
|
3. The D13 pin controls the output register on the '595 shift registers. The code for
|
|
this must be enabled in Configure.h. This pin is not connected when using the 74LS164.
|
|
|
|
The two shift registers can produce a sixteen bit address, although the 28C256 only needs
|
|
15 addresses. Chips larger than 64K are supported by using the shift registers for A<sub>0</sub>..A<sub>15</sub>
|
|
and connecting Arduino pins D10..D12 to the chip's A<sub>16</sub>..A<sub>18</sub>
|
|
|
|
|
|
|
|
**NOTE:**
|
|
The schematic does not show the Vcc and ground pins for the 74LS164 shift registers.
|
|
These must be connected to +5 and ground, respectively. It is also good practice to place a decoupling capacitor (0.1uF or 0.01uF is good) on the power rails near the Vcc connections.
|
|
|
|
## Ben Eater EEPROM Programmer
|
|
|
|
If you are here because you built the [Ben Eater EEPROM
|
|
Programmer](https://github.com/beneater/eeprom-programmer), note that the designs are
|
|
similar, but the TommyPROM code will not run on that hardware without some significant
|
|
changes. If you just need to unlock the Software Data Protection (SDP) on a chip, then
|
|
see the
|
|
[unlock-ben-eater-hardware sketch](https://github.com/TomNisbet/TommyPROM/tree/master/unlock-ben-eater-hardware) for a solution. That sketch is purpose-built to run on the Ben Eater
|
|
hardware directly and it will not work with the TommyPROM hardware.
|
|
|
|
If you want the functionality of the TommyPROM software on the Ben Eater hardware, the
|
|
easiest path is probably to modify the hardware to match the TommyPROM software rather
|
|
than trying to change the pin assignments in software. There are a few reasons for this:
|
|
|
|
* The Ben Eater hardware uses D13 to control the ROM's Write Enable pin and it ties the
|
|
Chip Enable pin to always be active. The D13 pin is connected to the Arduino's built-in
|
|
LED, which blinks at boot. This means that the chip is likely writing some random data at
|
|
boot time. This isn't a problem for the Ben Eater sketches, because they always write
|
|
their own data to the chip anyway. One use of TommyPROM is to just read data from a chip,
|
|
so a random write on boot would be bad.
|
|
* The OE pin is controlled by the Address shift registers. This doesn't work well with
|
|
the modular architecture of TommyPROM and it definitely would not work with 74LS164s
|
|
because it would toggle the OE pin as new addresses are shifted in.
|
|
* The direct port write software is a bit complicated and is more difficult to change than
|
|
just renaming a few pin #defines. This was done for performance reasons, particularly
|
|
for the SDP timing, but it means that the code is not easy to change.
|
|
|
|
Changing the hardware is fairly straightforward. The data lines move 3 pins from D5..D12
|
|
down to D2..D9. Most of the ROM and shift register control lines move over to the A0..A5
|
|
pins. The upper shift register is controlled directly from the Arduino instead of being
|
|
connected to the overflow of the lower shift register. All of the connections are in the
|
|
chart in the section above.
|
|
|
|
## Intel 8755A Hardware Version
|
|
|
|
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 additional 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.
|
|
|
|
|
|
|
|
Eagle-format schematics can be downloaded from the
|
|
[hardware project page](https://github.com/TomNisbet/TommyPROM/tree/master/hardware).
|