Consistent Data Access Without The Use Of Sfc 14 Or Sfc 15 - Siemens SIMATIC S7-400 Reference Manual

1.13.5

Consistent Data Access without the Use of SFC 14 or SFC 15

Consistent data access of > 4 bytes without using SFC 14 or SFC 15 is possible
for the CPUs listed below. The data area of a DP slave that should transfer
consistently is transferred to a process image partition. The information in this area
are therefore always consistent. You can subsequently use load/transfer
commands (such as L EW 1) to access the process image. This is an especially
convenient and efficient (low runtime load) way to access consistent data. This
allows efficient integration and configuration of drives or other DP slaves, for
example.
This applies to CPUs with firmware version 3.0 or later:
CPU 412-1
CPU 412-2
CPU 414-2
CPU 414-3
CPU 416-2
CPU 416-3
CPU 417-4
No I/O access error occurs with direct access (e.g. L PEW or T PAW).
The following is important for converting from the SFC14/15 method to the process
image method:
• When converting from the SFC14/15 method to the process image method, it is
not recommended to use the system functions and the process image at the
same time. Although the process image is updated when writing with the
system function SFC15, this is not the case when reading. In other words, the
consistency between the process image values and the values of the system
function SFC14 is not ensured.
• SFC 50 "RD_LGADR" outputs another address area with the SFC 14/15
method as with the process image method.
• If you are using a CP 443-5 ext the simultaneous use of SFC 14/15 and the
process image results in the following errors, you cannot read/write into the
process image and/or you can no longer read/write with SFC 14/15.
Automation System S7-400 CPU Specifications
A5E00165965-01
S7-400 CPU
Structure of a CPU 41x
MLFB
6ES7412-1XF03-0AB0
6ES7412-2XG00-0AB0
6ES7414-2XG03-0AB0
6ES7414-3XJ00-0AB0
6ES7416-2XK02-0AB0
6ES7416-3XL00-0AB0
6ES7417-4XL00-0AB0
1-71