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A-Z80 is a conceptual implementation of the venerable Zilog Z80 processor targeted to synthesize and run on a modern FPGA device. It differs from the existing (mostly Verilog) Z80 implementations in that it is designed from the ground up through the schematics and low-level gates.

...continue reading "A Z80 From the Ground Up"

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The data bus on the Z80 processor is 8 bits wide. Data bus wires carrying information within the chip itself do not simply connect to package pins and out to the world - the gate circuitry of each bit is quite complex. This article presents a transistor-level schematic of a data bit’s gate which I reverse-engineered from a die photograph.

Data pins (D0-D7) carry arguably the most complex signals on the Z80 since they are both bi-directional and capable of tri-stating. They are located around the +5V pin – four of them on each side. This is a microphotograph of a gate of one of the data pins which we will look at more closely today – a pin for a data line D6.

...continue reading "The Anatomy of a Z80 Gate"

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After reading excellent Ken Shirriff's blog on reverse-engineering parts of the Z80 CPU, I decided to learn how to decipher some of the chip die-shots myself. It turns out not to be that difficult if you follow certain guidelines, which I will describe in this post.

Start with a good and clean die shot. Although the Visual 6502 team had a good one, it was somewhat grainy, and I've found a much cleaner version here. There is a slight difference in masks, but the functions are the same. In fact, it may even help to look at several versions when trying to decipher the layout.

...continue reading "Z80 Instruction Register deciphered"

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In my previous post, I described an Arduino dongle and the software that can be used to clock a Z80 CPU and dump the states of its buses and pins while executing a controlled set of test cases.

Here I show a trace of every single Z80 instruction as run by that setup. I also outlined some of the tests created manually that clarified a few situations which were not too obvious (to me) after reading various pieces of documentation.

...continue reading "ZiLOG Z80 (un)documented behavior"

A few months ago I had ordered a new PCI parallel port card. It turned out my computer did not have a parallel port and I wanted to try the parallel port logic analyzer software described here:
http://www.codeproject.com/Articles/75279/17-Channel-Logic-Analyzer

...continue reading "Parallel Port Logic Analyzer"

I tried a simple software implementation of a digital oscilloscope using a PCI sound card and this software: http://www.zeitnitz.de/Christian/scope?mid=2

I connected its own signal generator (from the line out) into the line in and it worked -- sort of. The input capacitors were skewing low frequencies. I de-soldered those caps but then hit a bigger problem of a floating DC component. Also, there was a lot of noise on the line.

...continue reading "Software Scope using a Sound Card"

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A weather station, Ambient Weather WS-2080 that I installed in my backyard has a receiver unit with a pretty nasty hardware issue: occasionally, its USB interface would hard hang. It could happen twice a week or once a month – it is very unpredictable and highly annoying. Once it happens, nothing short of a power reset of the receiver unit would fix it. You’d have to remove the battery or unplug the USB if you powered it through it. I've finally got around to fixing it. If you have a similar problem with that weather station, you may be interested to read on...

...continue reading "Ambient Weather WS-2080 hang fix"

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Just before the Wold Cup, the most horrific thing happened: our 65" Mitsubishi WS-65819 broke!

Now, most people would run to the nearest TV store and purchase a brand new HD TV without blinking, but this mishap presented an opportunity to see what's inside that TV and to try to fix it.

...continue reading "Fixing convergence on TV"

(This article was first written in March 2009 - now most of us have Android tables laying around performing this task and much more!)

For a long time, I wanted to buy an internet radio to get access to thousands of stations from all over the world. However, it seemed the market in the US was way behind that of Europe, where (especially in the UK) you could select among many models of digital, Ethernet-equipped radios. Many of them had features such as pausing and recording the audio stream.

Aren't you also intrigued with these novel picture frames, but could never justify the price of one, with better models reaching hundreds of dollars and lesser models not really worth buying? Picture frames were one of the best-selling gifts in 2008, with an average price of $169 for a connected photo frame (EE Times, Feb 23rd, 2009), but people are mostly confused with the device. I've seen a few in people's homes being used for several weeks and then collecting dust.

...continue reading "Building a Custom Picture Frame"