Data Acquisition

After the counter is programmed the output will be high. Writing an initial count arms thecounter and a subsequent trigger loads the counter. The output goes low on the next clockpulse and remains low until the counter reaches zero. The output then goes high andremains high until the next clock pulse after the next trigger.An initial count of N results in a one-shot pulse N clock cycles long. The one-shot is retriggerable;hence the output will remain low for N clock pulses after any trigger. Theone-shot pulse can be repeated without rewriting the initial count to the counter. The gateinput has no effect on the output.If a new count is written to the counter during a one-shot pulse, the current one-shotpulse is not affected unless the counter is re-triggered. In that case, the counter is loadedwith the new count and the current one-shot pulse continues until the new count expires.After the counter is programmed the output will be high. An initial count of N is loadedon the next clock pulse and when it has decremented down to 1, the output goes low forone clock pulse. The output then goes high, the counter automatically reloads the initialcount and the process is repeated indefinitely. The sequence is repeated every N clockpulses.The gate input enables counting when high, and inhibits counting when low. If the gategoes low during an output pulse, the output is set high immediately. A trigger reloads theinitial count on the next clock pulse and the output goes low for one clock pulse after Nclock pulses. Thus, the gate input can be used to synchronize the counter.Writing a new count does not affect the current counting sequence. If a trigger issubsequently received before the end of the current period, the counter will be reloadedon the next clock pulse and counting will continue from the new count. Otherwise, thenew count will be loaded at the end of the current cycle. In this mode, an initial count of 1is invalid.Mode 2 functions like a divide by N counter. It can also be used to generate an outputfrequency or a periodic interrupt.Mode 3 is similar to mode 2 except for the duty cycle of the output. After the counter isprogrammed, the output will be high. An initial count of N is loaded on the next clockpulse. When half of the initial count has expired, the output goes low for the remainder ofthe count. The output then goes high, the counter automatically reloads the initial countand the process is repeated indefinitely. This results in a square wave with a period of Nclock cycles.The gate input enables counting when high, and inhibits counting when low. If the gategoes low when the output is low, the output is set high immediately. A trigger reloads thecounter with the initial count on the next clock pulse. Thus, the gate input can be used tosynchronize the counter.Writing a new count does not affect the current counting sequence. If a trigger issubsequently received before the end of the current half-cycle of the square wave, thecounter will be reloaded on the next clock pulse and counting will continue from the newcount. Otherwise, the new count will be loaded at the end of the current half-cycle.Mode 3 functions slightly differently for even and odd initial count values.