Configuration Notes:
The fundamental differences between the integrated DP interface of a CPU and the DP interface of the CP 342-5 are shown in the tables below.
 

Configured as	CP 342-5	CPU 315-2
DP master	In more recent releases of the CP 342-5/CP342-5 FO (6GK7 342-5DA01-0XE0, 6GK7 342-5DA02-0XE0 or 6GK7 342-5F00-0XE0), you can select the DP slaves directly from the standard catalog. The CP342-5 (6GK7 342-5DA00-0XE0) only supports standard slaves. Consequently, you can only use the slaves that are contained in the HW Catalog under "PROFIBUS-DP > CP 342-5 as DP-Master" or "PROFIBUS-DP > DP V0-Slaves". Whenever GSD files are used, please bear in mind that you can only use DP standard slaves here, too.	You can select all the DP slaves directly from the standard catalog.
DP slave	The I/O modules are configured via universal modules which are then adapted in accordance with the slave's actual I/O data.

Table 1: Differences in configuration

 

CP 342-5

CPU 315-2

Data transfer between the CPU and the CP takes place via special block calls (FC1 "DP_SEND" and FC2 "DP_RECV"). The user is free to select the source or target areas of the data being received or sent. You can use a data block, the bit memory address area or the I/O area for this. As the I/O area cannot be accessed directly, the I/O addresses may occur repeatedly if there is more than one CP in use. You can find a description of these blocks in the "SIMATIC NET NCM S7 for PROFIBUS" manual under Entry ID: 1158693.

As in centrally plugged-in modules, the DP slave data is located in the CPU's I/O area. This data can be accessed directly via load and transfer commands, such as "U E 1.0".

Table 2: Programming the data transfer

The volume of project data supported by the modules is release-dependent.
Various modules are compared in the table below:
 

DP master interface	Max. number of DP slaves	I/O area as a ...
		DP master	DP slave
CPU 315-2DP (6ES7 315-2AF03-0AB0)	64	1 KB	244 bytes
CPU 316-2DP (6ES7 316-2AG00-0BA0)	125	2 KB	244 bytes
CPU 318-2DP (6ES7 318-2AJ00-0AB0)	125	8 KB	244 bytes
CP 342-5 (6GK7 342-5DA00-0XE0)	124	240 bytes	86 bytes
CP 342-5 (6GK7 342-5DA02-0XE0)	124	2160 bytes	240 bytes

Table 3: Differences in the volume of project data

 

CP 342-5	CPU 315-2
The entire data area (up to 2160 bytes) can be regarded as consistent if the following procedure is followed: The received data can only be analyzed if the block signals that new data has been received error-free. The data being sent is left unchanged until the block reports that the data has been transmitted error-free. If the procedure differs, this results in a data consistency of 32 bytes.	SFC calls (SFC14/15) have to be used in order to transmit consistent data measuring 3 or 4 bytes in length. SFC14 "DPRD_DAT" is used to read and SFC15 "DPWR_DAT" is used to write consistent data. The maximum number of pieces of consistent data is dependent on the CPU used. You can find these details in the "CPU Data" manuals.

Table 4: Differences in consistent data

 

CP 342-5	CPU 315-2
CPs 342-5 (from 6GK7 342-5DA02-0XE0) or CPs 342-FO (6GK 342-5DF00-0XE0) support baud rates of up to 12 MB. Exception: CP 342-FO supports neither 3 nor 6 MB. Previous releases of CPs (6GK7 342-5DA00-0XE0 or 6GK7 342-5DA01-0XE0) only support baud rates of up to 1.5 MB.	The integrated interfaces of the CPU support baud rates of up to 12 MB.

Table 5: Differences in the supported baud rate

You can find further information about this topic in the following Entry IDs:
 

Topic:	Entry ID:
Frequent user errors when using the CP 342-5 as DP master	18208090
Version of the function blocks needed to operate a CP 342-5?	187699
What should you watch out for when upgrading the CP 342-5 or fitting spare parts?	7806643
CP342-5 manual	8773570
Manual "SIMATIC NET NCM S7 for PROFIBUS", chapter 4 "DP Master Mode"	1158693