Siemens S5-155U System Manual page 268

System Manual
C79000-B8576-C199-03
Communication memory
The communication memory comprises a central battery-backed RAM
in the PLC. It has three areas: 1) the communication flags (256 bytes),
2) the semaphores (32), and 3) four memory pages.
The communication flags are located in memory area F200H to
F2FFH. The communication flags enable the cyclic interchange of
small volumes of data between the CPUs in the S5-135U/155U PLC.
The four memory pages serve for the exchange of data blocks between
CPUs.
Please consult the Programming Guides of the CPUs to program these
two functions.
The semaphores are used to coordinate the CPUs for access to the
same I/O address (see Programming Guides, operations SES and
SEF).
F200H
Communication Flags
F300H
Synchronization
Area for
Operating Systems
F400H
Page No.
Page Memory for
252
Data Blocks
F7FFH
Vector Register
for Page Selection,
FEFFH
Fault Register
Figure 6-8 Areas of the Communication Memory on the S5 Bus
Addressing method for the page memory (vector register)
The vector register serves to form subaddresses of several memories
in a common address area. The register is an 8-bit register which is
written to under address FEFFH. It cannot be read out.
The page memory contains four pages of 1 Kbyte. An identification
number is assigned to each page. These are the numbers 252, 253,
254 and 255.
923C Coordinator Module
Page No. Page No. Page No.
253 254 255
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