Accessing As-I Analog Data Via The Process Image; Accessing As-I Analog Data Via Acyclic Services - Siemens SIMATIC ET 200SP Manual

Data exchange between the user program and AS-i slaves
7.3 AS-i analog values and transparent / digital values more than 4 bits in length are transferred
7.3.1

Accessing AS-i analog data via the process image

If you assigned I/O addresses to the analog slaves when configuring, you can access the
AS-i analog values with word commands (Firmware V1.1 and higher).
Analog and transparent I/O addresses for configured AS-i slaves
The analog and transparent I/O addresses of an AS-i slave can be freely assigned within the
overall process image of the CM AS-i Master ST. This is regardless of the size of the
process image. If you only require a few analog inputs and outputs in the process image and
want to save space, you can change the length of the I/O data of an AS-i slave. If the set
length is less than the actual length of the I/O data of the AS-i slaves, you cannot access the
data at addresses greater than the set length via the process image. You can also deactivate
the process image for analog inputs/outputs. Please also see the description of the options
"Sorting" and "Packing" in Section I/O addresses when configuring AS-i slaves in STEP 7
(Page 46).
Access to analog I/O data is also possible via data records independent of the process
image. You can find more detailed information on this in Section "Accessing AS-i analog
data via acyclic services (Page 58)".
7.3.2

Accessing AS-i analog data via acyclic services

Representation of the analog values in the data records
Analog values are transferred in the data records numbered from 140 to 147.
● You access the analog input values using system functions for reading data records.
● You output analog values using system functions for writing data records.
In combination with SIMATIC S7, system function blocks SFB 52 "RDREC" and SFB 53
"WRREC" enable this.
Access to analog data via acyclic services can also be selected, for example, if there is a
need to save I/O address space in SIMATIC S7.
NOTICE
Simultaneous write access via cyclic and acyclic services not possible
Simultaneous write access to analog data of a slave is not permissible with different
process values either via cyclic or acyclic services. If both services are used the analog
output values that are output via cyclic and acyclic services to the same slave address must
be synchronized with each other via the user program.
You can use data record lengths ranging from 2 bytes to 240 bytes for each data record
number. For each slave address, an area of 8 bytes is available to address 4 analog
channels.
58
AS-Interface master CM AS-i Master ST (3RK7137-6SA00-0BC1)
Manual, 07/2017, A5E02655262020A/RS-AD/004