Deck 12: Programming Counters

Question 1

Explain the Count Up Enable Bit (CU).

Answer 1

The CU bit (bit 15) is set to 1, or is true, when the rung is true, and remains true as long as the up counter is enabled. The CU bit goes false when the counter is reset or the counter rung goes false. The CU bit is only used with up counters.

Question 2

Explain the Count Down Underflow Bit (UN).

Answer 2

The UN bit (bit 11) is set by the processor to 1, or ON, when the accumulated count exceeds the lower limit of (-)32,768. It wraps around to (+)32,767, and the
CTD instruction counts down from there.

Question 3

The up counter consists of a counter block that contains the up counter address, the preset value, and the accumulated count value which can be any number from 0 to ____________________.

Answer 3

+32,767,32,767

Question 4

The same CU, CD, DN, OV, and UN bits are available on the Logix5000 counters as was available on the other Allen-Bradley counters.

Question 5

PLC-5 can have counter numbers from 0 through 999, and each counter requires ____________________ words of memory.

Question 6

In addition to the instructions in other Allen-Bradley counters, Logix5000 controllers have the counter instruction ____________________. This is both an up and down counter in one instruction with a built in reset function.

Question 7

If the accumulated value should exceed the upper limit, the overflow bit (OV) will be set and the counter then rolls over to -2,147,483,647 and begins counting up again.

Question 8

The Allen-Bradley up counter format is similar to the ____________________ format.

Question 9

Allen-Bradley offers two types of counters: up counters (CTU) and down counters (CTD).

Question 10

Explain the Count Up Overflow Bit (OV).

Question 11

The Allen-Bradley up counter consists of a counter block that contains the up counter address, the preset value, and the ____________________ value.

Question 12

Explain the Count Enable Bit (CD).

Question 13

Explain the Count Done Bit (DN).

Question 14

Timers can be combined with counters when it is necessary to extend the time of the timer beyond its normal limits.

Question 15

By only having one counter file, the MicroLogix 1000 is limited to 64 counters (counters 0 through 63).