Sfc 81 “Ublkmov”; Consistency For Communication Blocks And Functions - Siemens SIMATIC S7-400H Manual

SFC 81 "UBLKMOV"
With SFC 81 "UBLKMOV" (uninterruptible block move), you can copy the contents
of a memory area (= source area) consistently to a different memory area (=
destination area). The copy operation cannot be interrupted by other operating
system activities.
SFC 81 "UBLKMOV" enables you to copy the following memory areas:
• Memory markers
• DB contents
• Process image of the inputs
• Process image of outputs
The maximum amount of data you can copy is 512 bytes. Take into consideration
the restrictions for the specific CPU, which are documented in the operations list,
for example.
Since copying cannot be interrupted, the interrupt reaction times of your CPU may
increase when using SFC 81 "UBLKMOV".
The source and destination areas must not overlap. If the specified destination
area is larger than the source area, the function only copies as much data to the
destination area as that contained in the source 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.
4.10.1

Consistency for Communication Blocks and Functions

Using S7–400 the communication data is not processed in the scan cycle
checkpoint; instead, this data is processed in fixed time slices during the program
cycle.
On the system side only the commands byte, word and double word can be
processed in an intrinsically consistent way, in other words they cannot be
interrupted by communication functions.
When communications blocks, which are only used in pairs (such as SFB 12
"BSEND" and SFB 13 "BRCV"), are invoked in the user program and access
shared data, access to this data area can be coordinated by means of the "DONE"
parameter, for example. Data consistency of the communication areas transmitted
locally with a communication block can thus be ensured in the user program.
S7 communication functions such as SFB 14 "GET", SFB 15 "PUT" react
differently because no block is needed in the user program of the destination
device. In this case the size of data consistency has to be taken into account
beforehand during the programming phase.
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
Installation of a CPU 41x-H
4-41