Rockwell-automation 1772-LP3 PLC - 2/30 Programmable Controller Progra Uživatelský manuál stáhnout pdf (Strana 110)

100

101

Timer and Counter Instructions

Chapter 5

512

The Down-Counter (CTD) instruction subtracts one from its Accumulated

Value for each false-to-true transition of its rung conditions (Figure 5.9).

Because only the false-to-true transition causes a count to be made, rung

conditions must go from true to false and back to true before the next count

is registered.

Figure 5.9

DownCounter

Instruction

||

(

CTD )

113 054

PR 100

AC 150

The CTD accumulated value is retained when:

Mode Select Switch is changed to the PROGRAM position

Rung conditions go false

Power outage occurs provided memory backup power is maintained for

CMOS RAM memory

Each time the CTD rung goes true, bit 16, the enabled bit, is set on. When

the Accumulated Value is greater than or equal to the Preset Value, bit 15 is

set on. When the Accumulated Value goes below 000, bit 14 is set on to

indicate an underflow condition and the CTD continues down-counting

from 999.

Normally, the Down-Counter instruction is paired with the Up-Counter

instruction to form an Up/Down Counter, using the same word address,

AC value and PR value (Figure 5.10).

5.2.3

DownCounter Instruction

1 2 ... 105 106 107 108 109 110 111 112 113 114 115 ... 345 346

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