30. What instructions are needed to program counter 0 for binary counting in mode 4. The initial count is 2358H. Assume the base port address is B0H?
Answers
Answer:
We saw previously that toggle T-type flip flops can be used as individual divide-by-two counters. If we connect together several toggle flip-flops in a series chain we can produce a digital counter which stores or display the number of times a particular count sequence has occurred.
Clocked T-type flip-flops act as a binary divide-by-two counter and in asynchronous counters, the output of one counting stage provides the clock pulse for the next stage. Then a flip-flop counter has two possible output states and by adding more flip-flop stages, we can make a divide-by-2N counter. But the problem with 4-bit binary counters is that they count from 0000 to 1111. That is from 0 to 15 in decimal.
To make a digital counter which counts from 1 to 10, we need to have the counter count only the binary numbers 0000 to 1001. That is from 0 to 9 in decimal and fortunately for us, counting circuits are readily available as integrated circuits with one such circuit being the Asynchronous 74LS90 Decade Counter.
Digital counters count upwards from zero to some pre-determined count value on the application of a clock signal. Once the count value is reached, resetting them returns the counter back to zero to start again.