Pattern Generator for Bench Test of Digital Boards
- Saturday, 01 December 2012
Fresh data is streamed continuously for many tens of seconds with no gaps at 40 MHz.
All efforts to develop electronic equipment reach a stage where they need a board test station for each board. The SMAP digital system consists of three board types that interact with each other using interfaces with critical timing. Each board needs to be tested individually before combining into the integrated digital electronics system. Each board needs critical timing signals from the others to be able to operate. A bench test system was developed to support test of each board. The test system produces all the outputs of the control and timing unit, and is delivered much earlier than the timing unit.
Timing signals are treated as data. A large file is generated containing the state of every timing signal at any instant. This file is streamed out to an IO card, which is wired directly to the device-under-test (DUT) input pins. This provides a flexible test environment that can be adapted to any of the boards required to test in a standalone configuration. The problem of generating the critical timing signals is then transferred from a hardware problem to a software problem where it is more easily dealt with.
The first board to be tested was the ADC Digital Processor board (ADP). The ADP needed a complex Xilinx configuration data stream to operate, plus timing signals. The IO card is wired directly to the configuration and timing inputs of the board through VME connectors. A slower pattern maker program combines the Xilinx configuration and desired timing into a large data file. This data file is clocked out at 40 MHz (32 bits of data) into 28 inputs of the ADP to make it run.
The formatter board needs data from an ADP, plus timing information from the control and timing unit. Data captured from the ADP in its standalone test is combined with timing information into a large file. The large file streams out the IO card and is wired to formatter inputs. Since the formatter has more inputs than the IO card has bits, several signals were crossstrapped (duplicated), making it appear to the formatter that it was receiving two ADP boards when it was in fact receiving two copies of the same ADP board. In combined ADP/formatter integration, the IO card emulates the timing unit only.
Using IO cards to emulate missing hardware for bench test is an older technology. The improvement here is the ability to stream out fresh data continuously for many tens of seconds with no gaps at 40 MHz. This allows precise control over timing with time tag information that varies over a wide range. This allows a much better bench test than would have been possible in short pulses.
By allowing more complete testing of the individual boards when they are ready rather than deferring test to integration, the delivery of the SMAP digital system is accelerated.
This work was done by Andrew C. Berkun and Anhua J. Chu of Caltech for NASA’s Jet Propulsion Laboratory.
This Brief includes a Technical Support Package (TSP).
Pattern Generator for Bench Test of Digital Boards (reference NPO-48231) is currently available for download from the TSP library.
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