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Entry type: FAQ Entry ID: 21628388, Entry date: 06/20/2005

What are the differences between an integrated DP interface of my CPU (e.g. CPU 315-2 DP) and the DP interface of the CP 342-5?

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Configuration Notes:
The fundamental differences are shown in the tables below.

Configured as... CP 342-5 CPU 315-2
DP master In the case of later versions of CP 342-5/CP 342-5 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 CP 342-5 
(6GK7 342-5DA00-0XE0) supports only 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
Communications between the CPU and the CP are made via special block calls (FC 1 "DP_SEND" and FC 2 "DP_RECV"). The user is free to select the source or target areas of the data to be received or sent respectively. You can use a data block, the marker 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.

A description of these blocks is available in the "SIMATIC NET NCM S7 for PROFIBUS" manual in 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 342-5DA01-0XE0)
124 2160 bytes 240 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 evaluated if the block signals that new data has been received error-free.
  • The data being sent is left unchanged until the block signals 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 of a length of 3 or 4 bytes. 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. These details are available in the "CPU Data" manuals.

Table 4: Differences in consistent data
CP 342-5 CPU 315-2
The CPs 342-5 (from 6GK7 342-5DA02-0XE0) or the Cps 342-FO (6GK 342-5DF00-0XE0) support baud rates of up to 
12 Mbaud

CP 342-FO supports neither 3 nor 6 Mbaud.

Previous releases of Cps 
(6GK7 342-5DA00-0XE0 and 
 6GK7 342-5DA01-0XE0) only support baud rates of up to 1.5 Mbaud.

The integrated interfaces of the CPU support baud rates of up to 12 Mbaud.
Table 5: Differences in the baud rates supported

More information on this topic is available in the device manual "S7 Cps for PROFIBUS" in Entry ID 8773570 and in the manual "SIMATIC NET NCM S7 for PROFIBUS" (in the section entitled "DP Master Mode") in Entry ID 1158693.

FAQ 689920 has been incorporated into the present FAQ and deleted as a separate FAQ.

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