Logic Analyzers

During the 90’s I was in need of a fast and cheap way to analyze digital signals to a LCD display, I started on creating a way to do this via the PC’s Printer port. First I needed a interface for reading. During a Micro controller project I learned about Bidirectional settings of the printer port. Creating an interface to read all 8 data bits and all 5 status bits from it, was easy.

The schematics gives two possibilities in connecting the interface to the hardware.
– Directly, which is not a very good option.
– With using the 74LS245 or 244 as a buffer, as I used.  
– Buffers with OPTO Couplers which is the safest.

Because the printer port has no 5V supply line, you would need one external. In most cases, because of the low current, the circuit to be analized can be used as a supply.

Having the interface on a breadboard, I started on the software. My first choice was a VB6 program, that could scan the lines and review them. I wrote it around two Printer port libraries, inpout.dll and Win95io.dll, to see the speed differences.

The LogAna.exe scan routines reads the data and status ports, 2048000 bytes each, to memory.

While scanning I found that the speed was much to slow for my needs. My next option was to create a MSDOS program in assembly, writing bytes to the hard disc during reading the port.

The scanning can be done with visible signals on the screen or without, which makes it faster. With the /d option files can be read back and are shown like the screen shot on the right.

The software can be downloaded here as a complete package, both LogAna.exe and LA.COM, with all the sources.

Then, later, in 2014, creating tools with micro controllers, I created a 2.2″ TFT 176*220 Color display on a PIC18F4550. First I started on a working USB bootloader.
Then I checked the function of getting a BMP file to the display via USB with a small VB6 program.

After all that I started on controlling the SD Card with the PICBASIC SDFS libraries. So, with the VB6 program, I can read any picture file, JPG or BMP, adjust them for the display and write them to a SD Card as a file. The PIC will display them in turn.

In the meanwhile I found a possible option to create a logic analyzer. The display’s have an 8 bit parallel interface so are quite fast.

Those displays are very cheap and a very nice addition to build tools with.

It has a USB connection for reprogramming or power. Two trigger inputs can provide a start point for displaying. Timing can be adjusted and it has a ultra fast mode. The MCU runs on 48 MHz so I think the fast mode scans at about 1 MHz

Check the video below. It shows some bitmap uploads to the display and the Logic Analyzer in action.

The software can be obtained by emailing me. If you need more info, let me know…….

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