Consistent data
9.1 Consistency of communication blocks and functions
S7-400H
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System Manual, 03/2012, A5E00267695-11
The source and destination areas must not overlap. If the specified destination area is larger
than the source area, the function only copies the amount of data contained in the source
area to the destination area. If the specified destination area is smaller than the source area,
the function only copies as much data as can be written to the destination area.
For information on SFC 81, refer to the corresponding online help and to the "System and
Standard Functions" manual.
9.1
Consistency of communication blocks and functions
On the S7-400H, communication jobs are not processed in the cycle control point but rather
in fixed time slices during the program cycle.
The byte, word and double word data formats can always be processed consistently in the
system, in other words, the transmission or processing of 1 byte, 1 word = 2 bytes or 1
double word = 4 bytes cannot be interrupted.
If the user program calls communication blocks, such as SFB 12 "BSEND" and SFB 13
"BRCV", which are only used in pairs and access shared data, access to this data area can
be coordinated by the user by means of the "DONE" parameter, for example. The
consistency of data transmitted locally with these communication blocks can thus be ensured
in the user program.
In contrast, S7 communication functions do not require a block such as SFB 14 "GET", SFB
15 "PUT", in the user program of the target device. Here, you must make allowance for the
volume of consistent data in the programming phase.
Access to work memory of the CPU
The communication functions of the operating system access the CPU's work memory in
fixed block lengths. Blocks for S7-400H CPUs have a variable length of up to 472 bytes.
This ensures that the interrupt response time is not prolonged due to communication load.
Because this access is performed asynchronously to the user program, you cannot transmit
an unlimited number of bytes of consistent data.
The rules to ensure data consistency are described below.
Содержание SIMATIC S7-400H
Страница 24: ...Preface 1 1 Preface S7 400H 24 System Manual 03 2012 A5E00267695 11 ...
Страница 46: ...Getting Started 4 5 Special layout features of SIMATIC Manager S7 400H 46 System Manual 03 2012 A5E00267695 11 ...
Страница 120: ...Memory concept 10 1 Overview of the memory concept of S7 400H CPUs S7 400H 120 System Manual 03 2012 A5E00267695 11 ...
Страница 258: ...Communication 14 8 General issues regarding communication S7 400H 258 System Manual 03 2012 A5E00267695 11 ...
Страница 354: ...Synchronization modules 18 3 Selecting fiber optic cables S7 400H 354 System Manual 03 2012 A5E00267695 11 ...
Страница 434: ...Technical data 20 6 Runtimes of the FCs and FBs for redundant I Os S7 400H 434 System Manual 03 2012 A5E00267695 11 ...
Страница 460: ...Function modules and communication processors supported by the S7 400H S7 400H 460 System Manual 03 2012 A5E00267695 11 ...