The old school concepts of doing full BIT (built in tests) for computer systems is not particularly applicable to embedded microprocessor systems. I know the opinion is shared by others as I see from several posts before this one.

I would like to express that there are a couple of tests that are useful to be included in a BIT function test. Here is a list of tests that I include in most of the microcontroller projects that I implement.

- CODE space checksum test. Verified via a small aassembly language module as part of the start up test.

- RAM memory test for XDATA type memory that may be present in a design. Note that testing internal DATA memory in an 8051 is mostly a useless test to perform because if RAM is bad the processor will most likely crash anyway.

- DISPLAY test that simply flashes the display elements on a product. Indicators would blink once and an LCD display would display a very quick pattern. These tests let a user/customer service agent/or test tech to visually ensure that the displays are functioning. For LCDs I like to have the display show an even and odd checkerboard right after powerup for 100 mSec each.

- Other tests related to the system hardware. An example might be if a device has a A/D and a D/A it can be nice to provide loop back from one D/A channel back to a spare A/D input.

Michael Karas