This was fun! I have built the TFLA, the acronym for The Fabulous Logic Analyzer.
Not my own design, here is the original design.
The TFLA is a 8 port logic analyzer. Connected to the parallel port ofÂ a fast PC, the sampling rate can reach 1 MHz, And that makes it usable for my 6502 systems! Also perfect to analyze serial transmission.
I made someÂ changes to the original design:
- Between the parallel port and the output of the buffer I added 1 K resistors. To protectÂ Â ports that are not bidirectional.
- Added a 100 ohm resistor between the inputÂ and Â the buffer. To protect the buffer.
- Added a 10k ohm resistor Â to ground at the input of the buffer. This makes sure an unconnected input is at null level.
- Power for the buffer IC is taken from the USB port. Also this +5V is brought to the outside, enough to provide power for experiments.
The buffer is a 74HCT245, a perfect low power high impedance buffer IC. Connection between the TFLA and the parallel port via a Centronics connector (from an old printer!) and a standard printer cable.
The connectors for the logic input signals are from Conrad (2.6 mm) 730599 – 89Â Â and 733628 – 89Â (PCB bus). The clips are from dealextreme.com. The simple circuit is built on a strip-board.
Here are the photos (click on a photo for a larger view):