In January of 2022 I developed an 8-bit ISA card that housed breadboard modules for easy prototyping on the ISA bus. Following a request to release the design, I have uploaded all files to Github under open-source hardware license.
In November of 2019 I taught myself how to use KiCad by practising with the creation of the ISA POST Card v2.0. It was a passable first attempt at using the software, but some annoying bugs were discovered on the circuit boards that were produced. Ever since that time I have been slowly refining the POST card design to the latest v5.1 revision. Join me for an overview of the long journey, and to finally share the design that I am happy with.
Some readers may recall an older article that I wrote showing how to emulate a 7 segment display decoder with HEX output functionality, using an ATF16V8B PLD chip. The PLD programming was designed in such a way to mimic the physical characteristics of the 74LS47 BCD to 7-segment decoder/driver IC.
In progressing the belated final release of my ISA POST card design, I found myself in need of the “Blanking Input” functionality of the 74LS47 that had thus far been unimplemented in the ATF16V8B code.
This article explores the latest iteration of ATF16V8B PLD code that adds Blanking Input functionality, to better mimic the 74LS47.
In seeking to improve my ISA POST card design, I became frustrated at the general lack of modern seven segment display decoders that could decode and display a hexadecimal output. Rather than buy an older second-hand decoder IC, I fell down the rabbit hole of programming a PLD device to accomplish the task.
I’ve had a recent reader comment asking for me to share the details of the Keystone 9202 bracket that I’ve used in my ISA POST card design.
This has prompted me to create a proper place on my Github account to better manage storage of files that I’m pleased to share with the community. See ausandavno on Github.
To answer this question about the Keystone 9202, I’ve placed a Kicad footprint file, and 3D STEP file in the following location: https://github.com/ausandavno/Kicad_Misc
The last post in this series covered the receipt of the Retro-CGA prototype circuit boards, and the soldering of all components onto one of the boards, making a completed prototype card:
This post covers the last step in preparing the card for use; the derivation of the character ROM and the loading of the character data into the ROM chip on the card.
The last post in this series showed some of the detail of the Retro-CGA as it has come together so far, and ended with the preparation of Gerber files in preparation of having some prototype boards fabricated.
After a week or two of waiting, the fabricated boards arrived in the mail. This post documents the assembly of one of the boards into a completed prototype.
The last post on the Retro-CGA showed the gradual progression from schematic design to board build-up, summarising a period of several busy weeks.
This post acts as a summary of that whole exercise, showing some of the board design detail. More progression is made towards board fabrication and testing.
The last post in this series covered aspects of the initial schematic design of the Retro-CGA. This post will crack on with the initial board design, using the magic of pictures to show the detail of the board build-up.
I hope that you enjoy seeing the progress thus far on the Retro-CGA.
In one of my last posts I pondered the journey required to create an open-source video card inspired by the CGA card that I had repaired, in an attempt to preserve its historically-significant legacy.
In this post I will share the progress I’ve made on undertaking that journey, using the various guiding principles discussed in the initial post.
In what I presume will take months of effort, let’s launch into the design of the “Retro-CGA”.