Pulse sequence generation for counter testing - has voltage controlled multivibrator coupled to divider chain and gating stage coupled to counter output

摘要

The testing of counter circuits requires that a preprogrammed test frequency is applied and a predetermined pulse sequence length used. The counter is preset when an enable signal is applied. Input pulses are supplied over a frequency division selector coupled to 2:1 divider stages. The pulse source is an astable multi-vibrator with voltage controlled frequency provided by a digital to analogue converter. The activation period of the multivibrator is fixed by a preselected trigger signal that is of a longer period than the required pulse sequence. The pulse sequence is transmitted to output over a delay and a gate controlled by a bistable that is set by the counter. The counter output is generated when the state has changed by a predetermined number of steps.