Principle Of Operation - Siemens SIMATIC S5 Manual

Start-Up, Tests, and Diagnostics
3.4 FMA Services
This section provides you with the following information:
• What is meant by FMA services
• Why FMA services are used
• Which FMA services are relevant for the L2 interface of the S5-95U
• How FMA services are called up
The prerequisites for understanding this section are:
• Knowledge of STEP 5 programming
• Knowledge of how to handle the L2-SEND and L2-RECEIVE function blocks (see chapter 5)
These special functions give you access to the management services. FMA stands for Field bus
MAnagement. FMA services serve to monitor both the network and the local stations.
The FMA services make it possible to diagnose all of the network stations.
The communications processor evaluates the data collected from the stations.
3.4.1

Principle of Operation

• A service request is sent to the communications processor by means of integral function block
FB L2-SEND (FB252) .
• If the FMA service requests information from another station (only FMA service FDL_STATUS)
- The communications processor scans the status of the other station .
- The other stations replies .
• The system waits for a reply (confirmation) to arrive from the communications processor.
In the meantime the control processor processes the user program. This way the waiting time
does not cause any additional cycle delay.
• The user program indicates that a confirmation has arrived from the communications processor.
• The confirmation is fetched by means of integral function block FB L2-RECEIVE (FB253) .
S5-95U (L2 station)
Control
processor
Operating system
User program
STEP 5
data elements
Figure 3-7. Principle of Operation of the Programmable Controller with SINEC L2 Interface
3-10
Communications
processor
Bus
FB L2-SEND with
monitoring
service request
and
diagnostic
function
FB L2-RECEIVE
with confirmation
S5-95U, SINEC L2
Bus L2 station
EWA 4NEB 812 6112-02