The Fb 253 Mailbox Transfer Block; The Fb 254 Synchronization Block - Siemens SIMATIC S5 Manual

Blocks
6.1.5

The FB 253 Mailbox Transfer Block

If you are using a SINEC L1 LAN, it is connected to the B subunits of the relevant S5-115Fs. The user
program accesses the Receive mailbox direct without the FB 253.
If you have installed a dual-bus SINEC L1 LAN, you will have two Receive mailboxes (Bus A and
Bus B). Call the 253 MBXT mailbox transfer block if you wish to exploit the fault tolerance of the
dual-channel SINEC L1 LAN. FB 253 copies the contents of the Receive mailbox of Bus A into the
Receive mailbox of Bus B if an error has been reported in connection with the data traffic of Bus B.
Your program must then access the Receive mailbox of Bus B. If the other bus also develops a fault,
the system responds with an error message and the PLC enters the STOP mode.
Call and Parameter Assignment
Parameter Meaning
QSLN Source slave
No.
6.1.6

The FB 254 Synchronization Block

The following are regularly synchronized during the operating system run:
• Updating of timers (beginning and end of the OS)
• Requests of the time interrupt OB 13 (every 20 ms)
• Requests of the process interrupt OB 2 (every 20 ms) ( 2.3.1)
• PG execution
• SINEC L1 requests (every 20 ms).
Call the FB 254 synchronization block every time you wish to synchronize these functions within
your program.
You can define which functions are to be synchronized with the SYNC parameter.
Note
If you implement interval monitoring for the interrupt handling calls in the user
program, you must also always use the SYNC parameter to synchronize user times
when synchronizing interrupt handling.
6-10
Type Data
Type
D KF
Any number between 1 and
30 can be given as the source
slave No., with the exception
of the number of the slave in
question. A Receive mailbox
for both SINEC L1 buses must
be defined for every source
slave.
Assignment
KF = 1 to 30
S5-115F Manual
STL
: JU FB 253
Name : AGF:MBXT
QSLN :
EWA 4NEB 811 6149-02