Logic Analyzer Adapter for Xilinx boards

Description

The Intronix Logicport is a small USB-based logic analyzer. It has 34 channels, two of which can be used as clock inputs, and does state analysis at 200 MHz. Sample depth without compression is 2048 samples per channel. While the Logicport is modest in specifications, for many tasks it may well be all you need. I mainly use the Logicport for Xilinx FPGA projects.

The Logicport connects to the system under test using one of three ways:

The Logicport comes standard with a 38-wire flying lead probe. These are 38 individual color-coded wires - 34 signal and 4 ground wires - which you connect one by one.
A 38-pin Mictor ("Matched Impedance Connector") adapter is also available.
The Logicport uses a standard 40-pin IDC connector, so you may be able to use a 40-wire IDE hard drive cable as test lead if clock frequencies are low enough and your cable short enough. If you use an IDE hard drive cable as test lead, make sure the IDE cable is a full 40-wire cable, and not one with pin 20 disabled.

Logicport logic analyzer with flying leads. To the right, the Mictor adapter.

Problem

Plugging 38 color-coded leads on 38 header pins on my Xilinx Development Board is time-consuming and error-prone.

Solution

Instead of connecting through a flying lead probe, connect through a custom adapter.

Benefits:

The adapter simply plugs into the target system. No flying leads.
The Logicport plugs into the adapter. No cables.

Xilinx to Logicport adapter
Adapter, front view.	Adapter, back view.

Adapter sitting on a Xilinx ML403, using the Xilinx Generic Interface (XGI) connector. Other Xilinx developments boards feature the same connector. Please note the XGI connector is non-polarized. Make sure you do not plug in the adapter upside-down. Plugging in the adapter upside-down will short some FPGA outputs to ground, possibly damaging them.

ML403 board, with logic analyzer sitting on adapter.

This setup allows you to look at 32 signals, a clock enable and a clock inside the FPGA in real time at reasonable cost.

Ground loops

When connecting the Logicport to a circuit, you are connecting the circuit ground to the PC ground through the USB cable. If circuit ground and PC ground have a different potential, connecting them produces a ground loop. This is a general problem, which may also occur in USB oscilloscopes, for instance.

A simple solution against ground loops, sufficient for occasional use, is using a notebook with the AC cord unplugged, running off the battery. My personal choice has been to put a 100VA isolation transformer Block TIM-100 between notebook and mains and forgetting all about ground loops. Connecting the notebook to the network using unshielded twisted pair ethernet does not break the isolation.

Availability

I neither manufacture nor sell these adapters. If you want one, you will have to make one yourself. If you wish to have the printed circuit board made for you, download the archive for the adapter and extract all files. Send the .brd file to a PCB house such as pcb-pool. The .brd file is an Eagle format file. Ask for a double-sided PCB with solder mask, no silkscreen, no electrical testing.

Downloads

The schematics and board layout can be downloaded:

Logicport adapter for Xilinx boards. Schematics and board layout. Board dimensions are 100 mm x 38 mm.
Sample Xilinx ISE project for ML403 board. Implements a 100 MHz ring counter.
Sample Xilinx ISE project for ML505 board. Implements a 100 MHz ring counter.

You can use the sample ISE project as a simple electrical test. You should get the following waveform:

Ring counter output.

Last update page: October 9, 2007

Koen De Vleeschauwer

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