18
Operation
Description of the Write Service
The write service requires 8 bytes in the output data for the
request, and 6 bytes in the input data for the response. This
structure is defined directly in the device database file as a
module. A write command is entered in the output data by setting
the bytes. The response is then returned in the input data. --
Output data (request) telegram:
Table 7
Input data (response) telegram
Table 8
The response becomes valid at the time when the polling number
has the same value in the response telegram as in the request
telegram. --
Description of the individual entries:
Entry
Data type
Description
Service
Byte
ID for write service (Index = 0x10).
This value can be entered once
before the first write job.- It is not
necessary to make an entry for
every write service to start. --
Poll. number
Byte
When this value is changed, the
write job will be executed. - As
long as this value remains
unchanged, the write job is not
executed any longer. -- Value 0 is
permissible.- It is useful to activate
a write job by incrementing the
value by 1. - A one byte overflow
from 0xFF to 0x00 is not a
problem.
Variable
index
16-bit integer
Index of variables that are to be
written.- Refer to section
"Addressing the Data" for a list of
possible indices. Only use the
same positive variable indices for
acyclic writing as for cyclic
reading. -
Entry
Data type
Description
Variable
index
Lowbyte
Byte
The low byte of the 16-bit integer value for
the variable index. --- In the
attached variable index list these
are the 2 right digits of the
hexadecimal number. ---- Only
necessary when the master
system does not allow to define a
16-bit integer. --
Variable
index
Highbyte
Byte
The high byte of the 16-bit integer value
for the variable index. -- In the
attached variable index list these
are the 2 digits to the right of
0x....... in hexadecimal format.
Only necessary when the master
system does not allow to define
16-bit integers. ------
1 to 4
Data bytes
4 bytesData block for REAL, DINT, TIME, INT and
BOOLean data
Status
Byte
0x01 is delivered as the status when the
job has been carried out without
errors. - The error field contains
the value 0x00. Otherwise, 0x00 is
delivered as the status. In this
case, the error cause can be
derived from the error field.
Error
Byte
Outputs information about the occurred
error, when the status field has the
value 0x00. Error codes:
0x00
No error.
0x40Unknown service entered in
the service field. --
0x20Unknown index entered in the
variable index field. -
Example
The value 65.0 is to be written acyclically to the manually
adjustable output value of the second control loop. The necessary
variable .L2_YHAND has the variable index 0x015B. With
byte-wise definition, 0x5B, 0x01 (low byte before high byte) must
be used. -
The REAL number 65.0 in byte format is: 0x00, 0x00, 0x82, 0x42.
This is valid if 0xFF has been entered in the DP parameter
definition as the 4th. byte. -
The byte value to be specified as the polling number must be
different from the byte value used before.
Assumption:
So far the byte value of the polling number was 8.
In this case, the following values have to be entered in the request
bytes:
Byte 0
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Word 1
Service
=0x10
Polling
number-
Variable index
1 to 4 data bytes
Service
=0x10
Polling
number-
Variable
index
Lowbyte -
Variable
index
Highbyte -
1 to 4 data bytes
Byte 0
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Word 1
Service
=0x10
Polling
number -
Variable index
Status
Error
Service
=0x10
Polling
number -
Variable
index
Lowbyte -
Variable
index
Highbyte -
Status
Error
