by using PC Parallel Port

(By Huzaifa S. Sidhpurwala, India)

This is one of the simplest circuit for a PC parallel port based DLA. The Circuit is mainly used to protect the port which is fabricated on the motherboard itself.

The IC 74LS04 is an inverter and acts as a buffer. The Zener is used for undervoltage and overvoltage protection. If a voltage > 5V appears on the input, The buffer will not transmit this voltage to the PC. In the case of a voltage < 0V, The Zener will break down and 0.7V will appear at the input, hence again protecting the PC.

The software consists of two parts a graphical interface which shows five digital waveforms,.Various features of the waveforms can be controlled by the software. There is also a text interface in which the circuit is used as a 4-Channel DLA. The software is in pascal , an executable version is also avaliable.

Digital Logic Analyzer Software

The software Developed for this purpose is pretty straight forward. It is written in Pascal, though I prefer C much better, it can easily be coded in C as well.

The program consists of two parts, One of the programs plots the digital waveforms at the input on the screen and emulates a digital Oscilloscope. Various factors of the waveform can be controlled viz, the sampling rate etc. The figure below shows a screen shot of the program

The second part of the software is a text interface. In this DLA mode one of the channels acts as an external clock. The inputs are sampled at the negative or the positive going edge of the clock, A 4-bit trigger is previously given. Three trigger modes are available. The pre-trigger and post-trigger data is available as a report and can later be analysed

The figure shows a screen shot of this program.