Question 1

Explain the Count Up Enable Bit (CU).

Accepted Answer

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).

Accepted Answer

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 ____________________.

Accepted Answer

+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.

Accepted Answer

The Logix5000 counters in Allen-Bradley PLCs have similar status bits (CU, CD, DN, OV, UN) as the older models, providing consistent functionality across different generations of controllers.

Question 5

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

Accepted Answer

The answer of PLC-5 can have counter numbers from 0...

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.

Accepted Answer

The answer of In addition to the instructions in other...

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.

Accepted Answer

The counter rolls over to -2,147,483,648 (not -2,147,483,647) when it exceeds the upper limit of a 32-bit signed integer, which ranges from -2,147,483,648 to 2,147,483,647.

Question 8

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

Accepted Answer

The answer of The Allen-Bradley up counter format is similar...

Question 9

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

Accepted Answer

Allen-Bradley programmable logic controllers (PLCs) indeed offer two types of counters: up counters (CTU), which increment the count value when the input condition transitions from false to true, and down counters (CTD), which decrement the count value under the same conditions.

Question 10

Explain the Count Up Overflow Bit (OV).

Accepted Answer

The answer of 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.

Accepted Answer

The answer of The Allen-Bradley up counter consists of a...

Question 12

Explain the Count Enable Bit (CD).

Accepted Answer

The answer of Explain the Count Enable Bit (CD)....

Question 13

Explain the Count Done Bit (DN).

Accepted Answer

The answer of 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.

Accepted Answer

Timers and counters can be combined in programmable logic controllers (PLCs) and other control systems to create more complex timing functions, such as extending the timing beyond the normal limits of a single timer. This allows for more flexibility in control logic design.

Question 15

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

Accepted Answer

The answer of By only having one counter file, the...

Quiz 12: Programming Counters