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MANUFACTURING TESTING

by George Martin

Start ı The Problem ı A Possible Solution ı Test Setup ı POP Quiz ı Final Exam ı Sources and PDF

FINAL EXAM

Now letıs look at testing a complex device attached to the micro. The specific device I need to test is an HDLC controller with DRAM attached behind that device. Obviously itıs a large complex device. But, broken down from a testing or troubleshooting point of view, itıs made up data and control signals coming from the micro, data and control signals between the controller and the DRAM, and then the HDLC specific input and output signals.

These types of devices typically have registers to control their configuration and operation. The first type of test I would perform is to write all the registers and then read them back and check for correctness. Donıt write and read each register because, if the device is defective, youıll likely be reading the values remaining on the data bus (the ones you just wrote). Look to see if you can use one of these registers as a register to write and read all data values. If the registers fail, itıs time to pull out the scope and look for the problem. If they pass, you need more sophisticated tests. The tests become more device specific, but basically they would start with simple functions and grow into the more complicated operations.

Take for example, the DRAM connected to the back of the HDLC controller. First, you need to set up the registers in the HDLC device to control the DRAM. You can view the DRAM refresh cycles without any DRAM test software. Then you can write the same DRAM test software that was just covered. This time, access would be through the HDLC device.

So, consider developing your test suite early in your product design cycle. Ask yourself how youıre going to test these units. Also, decide how youıre going to troubleshoot the units that fail in production. When the time comes, it will be a lot easier to implement those plans.

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