Siemens S7-300 appendix Consistent data

Appendix

A.1 Information about upgrading to a CPU 31xC or CPU 31x

A.1.8 Using consistent data areas in the process image of a DP slave system

Consistent data

The table below illustrates the points to consider with respect to communication in a DP master system if you want to transfer I/O areas with "Total length" consistency. You can transfer a maximum of 128 bytes of consistent data.

Table A-1	Consistent data
CPU 315-2 DP		CPU 315-2 DP	CPU 318-2 DP
(as of firmware 2.0.0),		(as of firmware 1.0.0),	(firmware >= 3.0)
CPU 317,		CPU 316-2 DP,
CPU 31xC		CPU 318-2 DP (firmware < 3.0)
The address area of consistent		Even if they exist in the process	You can choose whether or not
data in the process image is		image, consistent data is not	to update the address area of
automatically updated.		automatically updated.	consistent data in the process
To read and write consistent			image.
data, you can also use SFC 14		To read and write consistent data,	To read and write consistent
and SFC 15. If the address area		you must use SFC14 and 15.	data, you can also use SFC 14
of consistent data is not in the			and SFC 15.
process image, you must use			If the address area of
SFC 14 and SFC 15 to read
			consistent data is not in the
and write consistent data.
			process image, you must use
Direct access to consistent
			SFC 14 and SFC 15 to read
areas is also possible (e.g.			and write consistent data.
L PEW or T PAW).			Direct access to consistent
			areas is also possible (for
			example, L PEW or T PAW).

CPU 31xC and CPU 31x, Technical data	A-7
Manual, Edition 08/2004, A5E00105475-05