Programming - Siemens DP/AS-Interface Link 20E Manual

Data Exchange Between the DP Master and AS-i Slave
2.4.2

Programming

Job Parameters
Make the parameter settings for the read_record and write_record jobs as
described in Section 2.4.1. Access to the analog values is controlled by the
following parameters:
S Index:
Specifies the data record number in which the analog values are stored on the
DP/AS-i Link 20E. How the available data record numbers 140 to 147 are used
is explained below.
S Length:
Specifies the length of the input/output data area; the specified length must be
adapted to the data record being used and the address area of the analog
slaves. This is explained in greater detail and with examples below.
S Data:
Specifies the address of the input/output data area in which your user program
accesses the analog values or makes the analog values available.
You will find sample calls at the end of this chapter.
Data Consistency
In terms of one AS-i slave, the analog values transferred to the DP master are
always consistent.
Mapping the Analog Values in the Data Records
To access analog values, you can select one of the data records 140 to 147. The
data records differ from each other in their length. This allows you to optimize the
data area to be reserved in your application if you are using less AS-i analog
slaves than the maximum number supported by the interface.
An 8-byte area is used for each slave address to manage 4 analog channels.
Remember that slave address 31 is not used in data record 140.
Table 1-1 below shows which address area in the selectable data records the
analog values of which AS-i slave are transferred to. How the analog values of an
analog slave are mapped in the address areas is shown in Table 2-4.
The table can be used equally for the analog input area and the analog output
area.
Following the tables, you will find notes explaining how to read the tables.
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DP/AS-Interface Link 20E
Release 11/2002
C79000-G8976-C138–04