Description
The TTL Logic Probe is a simple diagnostic tool that. It help to troubleshoot an RC2014 or give a bit more of an insight in to what is going on. It is designed to plug in to the 5v and Ground sockets in the backplane with a flying probe lead that can either be plugged in to a signal on the backplane or touched against a component leg. The 3 LEDs will give an indication of the state of that signal.
Indications
- Logic Low (0 – 0.8v) is indicated by a green light
- Logic High (Anything above 0.8v, or open circuit) is indicated by a red light
- Activity (continuously changing state) is indicated by a solid yellow light. Green and red lights will give an indication of which is predominant.
- Momentary pulse is indicated by a 1 second pulse on the yellow light. The Green or red to show current state of the signal
This will not tell you exactly what is wrong with a non-running RC2014. However with some logical troubleshooting skills, it can point you in the right direction.
The TTL Logic Probe is great for getting an insight in to what is going on inside the circuit of an RC2014. For example, looking at the /Page pin of an RC2014 pro will see how this changes prior to loading CP/M as the ROM is paged out and the RAM is paged in. Probing the /CS pin of an IC will show you how often that chip is active.
Note that this probe is only suitable for 5v TTL circuits and any other voltages will either show incorrectly or result in damage. Note also that this is not a thorough debugging tool and will not pick up things like an incorrect clock speed or two devices trying to drive the same line both high and low simultaneously. For situations like that you will need more expensive test gear such as an oscilloscope.
