Siemens NAN 67 Series Manual de servicio descargar pdf (Pagina 124)

9-2

Ladder Logic (LAD) for S7-300 and S7-400

C79000-G7076-C504-02

9.1 Location of a Timer in Memory and Components of a Timer

Timers have an area reserved for them in the memory of your CPU. This

memory area reserves one 16-bit word for each timer address. The ladder

logic instruction set supports 256 timers. Please refer to your CPU’s technical

information to establish the number of timer words available.

The following functions have access to the timer memory area:

S Timer instructions

S Updating of timer words by means of clock timing. This function of your

CPU in the RUN mode decrements a given time value by one unit at the

interval designated by the time base until the time value is equal to zero.

Bits 0 through 9 of the timer word contain the time value in binary code. The

time value specifies a number of units. Time updating decrements the time

value by one unit at an interval designated by the time base. Decrementing

continues until the time value is equal to zero. You can load a time value into

the low word of accumulator 1 in binary, hexadecimal, or binary coded

decimal (BCD) format (see Figure 9-1). The time range is from 0 to 9,990

seconds.

You can pre-load a time value using either of the following formats:

S W#16#wxyz

– Where w = the time base (that is, the time interval or resolution)

– Where xyz = the time value in binary coded decimal format

S S5T# aH_bbM_ccS_ddMS

– Where a = hours, bb = minutes, cc = seconds, and dd = milliseconds

– The time base is selected automatically, and the value is rounded to

the next lower number with that time base.

The maximum time value that you can enter is 9,990 seconds, or

2H_46M_30S.

Bits 12 and 13 of the timer word contain the time base in binary code. The

time base defines the interval at which the time value is decremented by one

unit (see Table 9-1 and Figure 9-1). The smallest time base is 10 ms; the

largest is 10 s.

Table 9-1 Time Base and Its Binary Code

Time Base Binary Code for the Time Base

10 ms 00

100 ms 01

1s 10

10 s 11

Area in Memory

Time Value

Time Base

Timer Instructions

1 2 ... 119 120 121 122 123 124 125 126 127 128 129 ... 317 318

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