Siemens S5-135U/155U - Manual (Page 391)

9-9
System Manual
C79000-G8576-C199-06
In the selective sampling mode, a measured value is encoded on the central
initiative of the CPU. At the start of conversion, the module must be
addressed once with a write operation (T PW) by the user program. An active
bit (T = 1) is set during encoding.
With the transition to T = 0, the measured value becomes valid. With
non-constant cycle times, there may be non-periodic measured value
aquisition. If you operate the module in this mode, you must set a module
address from 128 to 255. You can also use the address range from 0 to 127
for selective sampling after appropriate programming in DB 1 of the user
program.
Another method is that of time-controlled program processing. With this
method, certain program segments (e.g. FB 13) are automatically inserted
into program processing at the 100 ms rate by a time-
controlled block (OB 13). A constant timebase is thus achieved.
FB 13 SPRM-B LEN=22 ABS
SHEET 1
SEGMENT 1
NAME: SELSAMPL EXAMPLE OF SELECTIVE SAMPLING
0005 :
0006 :
0007 :L PW128 READ ANALOG VALUE
0008 :T MW128 IN TO AUX: FLAG FW 128
0009 :A M 129.2 SCAN ACTIVITY =1?
000A :JC = END IF = 1, JUMP TO END
000B :T FW10 IF = 0, MEASURED VALUE IN FW 10
000C :T PB128 INITIATE SAMPLING
000D END : (1ST VALUE INVALID AFTER START)
000E
000F :
0010 :BE
You can read analog values of analog input modules with a function block
from the “basic functions” package.
The BASP signal is not interpreted by the 460 analog input module.
Selective Sampling
Time-Controlled
Program
Processing
Function Block
BASP (Output
Inhibit)
Analog Input/Output Modules