Reading Updated Bus Parameters (Read_Value) - Siemens SIMATIC S5 Manual

S5-95U, SINEC L2
3.4.7

Reading Updated Bus Parameters (READ_VALUE)

The READ_VALUE service allows you to read out the updated bus parameters of the local station.
Structure the READ_VALUE
request block as follows:
Request Block
Byte
0 com_class
FMA_Request=00
(service request)
1 user_id
Freely assignable ID. That ID is returned
unchanged in the confirmation.
2 service_code
Type of service requested
READ_VALUE
3-7 irrelevant
Relevant
parameters
Figure 3-14. Structure of the READ_VALUE Request and Confirmation Blocks
link_status
Table 3-7. link_status Messages for the READ_VALUE Confirmation
link_status Message
00
H
EWA 4NEB 812 6112-02
H
= 0B
H
ok (okay): Positive acknowledgement, service was executed,
bus parameters were read out
Start-Up, Tests, and Diagnostics
The data are stored in the READ_VALUE
confirmation block as follows:
Confirmation Block
Byte
0 com_class
FMA_Confirmation=01
(tacknowledgment from firmware following
FMA_Request)
1 user_id
ID assigned in the FMA_Request
2 service_code
Type of service provided by the firmware
READ_VALUE
3 link_status
4 irrelevant
5 irrelevant
6 irrelevant
7 irrelevant
8
Bus parameter block
(see Table 3-8)
9
......
Significance
H
= 0B
H
....
3-21