The design and development of a personal computer-based logic analyzer

With the low-cost, general-purpose computing power readily available in the form of the personal computer, a new type of laboratory instrumentation is evolving. Instead of each instrument being selfcontained, i.e., providing all of the hardware and "smarts" required for the collection, analysis, and display of data, the personal computer is used as the central controller for a variety of instruments. Each instrument then consists only of the hardware required to perform its specific function. The operation of the instrument is directed by the personal computer, thereby lowering its cost significantly.

Along these lines, a 16-channel, logic state analyzer was designed, developed, and tested. This logic analyzer consists of a personality module and probe pod interfaced to a personal computer, along with a software package to be run on the computer. The instrument is capable of triggering on any combination of low, high, or don't care logic states on the sixteen inputs, and provides memory for the storage of 256 samples occurring before or after the trigger input. A moveable "display slice" of 46 of the data samples can be displayed on the screen of the computer.

The system developed used a combination of Basic and assembly language software requiring 9K bytes of program memory. Cost for the hardware, not including the computer, is estimated at $150. The sample rate is specified as 3.3 MHz over the temperature range 0°C to 70°C; however, at room temperature the logic analyzer performed at sample rates to 14 MHz.

The design presented in this paper is intended as a first prototype of a new instrument. Possibilities for the expansion or modification of the design as presented are many. Some possible enhancements to the system are presented in Chapter IV, but these are only a few of many possibilities that exist with this new architecture of instrumentation.