faultfinding probe for uPs

r mi■ ,u(i(1,t 1985 1001111100111E 2 RI a 15.1B.410 faultfinding probe for /11)s Anyone who has ever tried to faultfind in a microprocessor system with a test probe will have experienced the uselessness of it. This is because the signals at the address, data, and con- trol buses are constantly — and rap- idly — changing. This means that it is not just the signal level that is import- ant, but also the instant the signals are present. For faultfinding properly, you need a logic analyser, which is capable of indicating several signals simultaneously. If you have no logic analyser, the probe presented here may provide the solution. Strictly speaking, this is nothing more than a bistable multivibrator (FF1). Data are simply read direct and cause D1to light or stay out, depending on the state of FF1. The bistable only reads at the instant its clock input (pin 3) switches from low to high. The clock signal is thus the key for all measurements carried out with the probe and that me...