Articles by Big Mess o' Wires

While I await the new Yellowstone v2.1 PCBs, I’ve been spending more time on testing. With my hacked-up v2.0 PCB, most things are working pretty well, especially with DOS3.3, ProDOS, or game disks. I can connect any odd combination of drives to the Yellowstone card, and expect that it will …

Throughout Yellowstone’s development, I’ve struggled on and off with mysterious problems related to the JTAG programmer. When the programmer is connected to the Yellowstone card, and I turn the computer off and on again, strange things sometimes happen. The Apple IIGS will boot to a screen of green and pink …

Throughout Yellowstone’s development, I’ve struggled on and off with mysterious problems related to the JTAG programmer. When the programmer is connected to the Yellowstone card, and I turn the computer off and on again, strange things sometimes happen. The Apple IIGS will boot to a screen of green and pink …

July 21, 2017 – I began the first work on what would become Yellowstone, with some attempts at designing a Verilog model of Apple’s IWM chip. Four years have passed since then, and I’m still working on this project! Today version 2.1 of the Yellowstone PCB is nearly ready …

I’m working on what I hope will be the final hardware changes for the Yellowstone 2.1 PCB. Among these are changes to my capacitor usage and placement strategy. In my previous posts I discussed intermittent problems that looked to be caused by ground bounce, VCC sag, or both. Apple II …

I’ve been searching for a simple and reliable way to prevent a short-circuit on Yellowstone’s -12V supply when a particular type of Macintosh disk drive is connected. Connecting this drive results in a +5V to -12V short circuit, but if the short is removed, the drive otherwise works just fine. …

I’ve returned to the question of how best to limit the current from Yellowstone’s -12V supply. I discussed this earlier here and here, and had more-or-less settled on the idea of using a current mirror circuit. But now I’m taking a second look at possibly using JFETs or a purpose-designed …

I’ve written several times about Yellowstone’s need for in-system FPGA reprogramming. Once the Yellowstone card is in the user’s hands, the user needs a way to update the FPGA firmware when new versions are released, without requiring a JTAG programmer or some kind of USB interface built into the …

The Yellowstone disk controller’s whole reason for existence is its ability to control any type of Apple II disk drive, but for a few Apple II programs, this universality causes problems. Yellowstone handles standard 5.25 inch drives just fine, but some software gets confused when it doesn’t find the ROM …

I’ve fallen into a deep hole involving current-limiting circuits and current sources, in an attempt to solve a minor problem with the Yellowstone disk controller. In the big scheme of things, this isn’t a very important problem, but it has me intrigued. I’ve created a simulation of a circuit …