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 of 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 some changes to the original design:
- Between the parallel port and the output of the buffer I added 1 K resistors. To protect PC ports that are not bidirectional.
- Added 100 ohm resistors between the input and the buffer. To protect the buffer.
- Added 10k ohm resistors 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 - 89 and 733628 - 89 (PCB bus). The clips are from dealextreme.com. The simple circuit is built on a strip-board.
Here are the photos: