Synchronous up/down Counters
The first class period
Review of “Basic Electrical Measuring Instruments”. 10
Topical content: Synchronous up-down counters. 10
Grammar item: Infinitive.
Text Synchronous up/down Counters
1. Synchronous up/down counters count number of pulses applied on the clock input. They consist of flip-flops and steering logic. (Fig. 3).
| Clock pulses Inputs clear InputsLoad input | A | Ha | data ( outputs-h Carry and > borrow |
| в | >ав |
| C | °-c |
| D | |
| >UP |
| yiJownCLRLoad | Carry |
| Fig. 3. Synchronous up/down counters |
2. The reversible counters have the; following inputs and outputs: clock pulses inputs for counting down and counting up; clear input for resetting counter at any time; data and load inputs for presetting counter to desirable initial number before co-
Data
inputs
output for indicating overflow of counter and borrow output for indicating underflow of counter.
3. The outputs of all flip-flops are triggered by a low-to-high level transition of either count (clock) input. The direction of counting is determined by which count input is pulsed while the other count input is high.
4. Counters are fully programmable, that is each output may be preset to either level by entering the desired data at the data inputs while the load input is low.
5. The output will change to agree with data inputs independently of the count pulses. This feature allows the counters to be used as module-N dividers by simply modifying the count length with preset inputs.
6. A clear input forces all outputs to the low level when a low level is-applied to this input. The clear function is independent of the count and load inputs.
7. The counters are designed to be cascaded. Both borrow and carry outputs are available to cascade both the up and down counting functions. The borrow output produces a pulse when the counter underflows. Similarly thd carry output produces a pulse when overflow occurs.
8. The counters can be easily cascaded by feeding the borrow and carry outputs to the count-down and count-up inputs respectively of the succeeding counter.
1 5
Read the text and write 7 names of inputs and outputs of counters.
2 3
Looking through the text find and read the passages containing the information:
а) о назначении реверсивных счетчиков;
б) об их устройстве;
в) об изменении выходного сигнала триггеров;
г) о каскадировании счетчиков.
3 3
Read the text paying attention to the Infinitives.
4 5
Repeat the words after the teacher. Then read them by yourself paying attention to their Russian equivalents.