Up/down counter control

by R v Linden 161UP/DOWN counter control The up/down binary- or BCD-mode counter is a regularly spotted item in digital circuits of various levels of complexity. The up/down counter simply does what its name indicates; it counts up or down, depending on the logic level applied at the relevant control input, and activates the corre- sponding output bit pattern at every pulse transition detected at the chip"s clock input. This circuit simplifies the control of up/down counters in that it allows the user to press one button to increment the counter output state, while another decrements it. Each of the changeover type buttons is connec- ted to a two-gate debouncer/bistable (111-N2 and N3-N4), which supplies a low pulse at its output when the rel- evant button is pressed. N8, which serves as an OR gate, receives the debouncer pulses and, together with N8, provides the output clock pulse to the up/down counter. Bistable Ns-Ns keeps track of the selected count mode, and provides the rel...