Instructions
The S7-200 can be incorporated as slave in a PROFIBUS DP network with the EM277 module. The process is described below taking the example of an S7-226 (slave) connected to an S7-314C-2 DP (master).

The figure below shows the sample configuration:

Fig. 01

Configuration of the slave (S7-200)
The activities here are limited to setting the PROFIBUS DP address that must match the configuration in the master.
 

No.	Procedure
1	Switch off the module's power supply.
2	Set the defined PROFIBUS DP address on the EM277. To do this you turn the lower address switch so that the arrow points to the desired number ("3" in the sample configuration). Fig. 02
3	Switch the module's power supply on again.

Note
A newly set PROFIBUS DP is recognized only after turning the power supply on.

Configuration of the master (S7-300)

Here you integrate the EM277 module in your S7-300 configuration, connect it to the PROFIBUS DP and configure the data communication between master and slave.
 

No.	Procedure
1	Create a new project in the SIMATIC Manager.
2	Insert an S7-300 station and a PROFIBUS DP network in the new project.
3	Open the "HW Config" editor and insert a channel, power supply and a CPU 314C-2 DP. Connect the CPU to the PROFIBUS DP segment. Fig. 03
4	You must integrate the EM277 in the hardware catalog of STEP 7 afterwards using a GSD file, because it is not included by default. The GSD file for the EM277 is located in the Internet on the SIMATIC Customer Support website in Entry ID: 113652. Detailed instructions on how to import a GSD file in STEP 7 are available in Entry ID: 2383630.
5	To find the new module quickly you can use the Find function in the hardware catalog. Fig. 04
6	Shift the EM277 module to the PROFIBUS DP segment and set the address of the slave. The address is "3" in the sample configuration.
7	For data communication between master and slave you must define the address areas for receive and send data on both sides. In the S7-200 these areas are in the variable memory. For the sample configuration we have defined a data length of 2 bytes for receive and send data. The following address areas have been selected: Receive area S7-300: EB10 and EB11 Send area S7-300: AB10 and AB11 Receive area S7-200:  VB100 and VB101 Send area S7-200: VB102 and VB103 Fig. 05 Add the relevant input/output module (2 Bytes Out / 2 Bytes In) from the hardware catalog according to the receive and send areas selected.
8	Change the addresses for the receive area (input) and send area (output) of the S7-300 appropriately. Also specify the type of data consistency to be used for data communication according to the input/output module selected. Fig. 06
9	Open the Properties window of the EM277 module and specify the start address of the receive area with the parameter I/O Offset in the V Memory. VB100 has been chosen as address in the sample configuration. The system automatically attaches the send area behind the receive area so you do not have to do this manually. Fig. 07
10	Save and compile the configuration and load it in the CPU 314C-2 DP.

Note
In the case of data communication the data sent by the master is stored in the receive area of the slave (variables memory). The user program of the S7-200 CPU must "save" this data to another data area, because otherwise it will be overwritten at the next send procedure. While the user program is processing the data in the variable memory cannot be overwritten. This is possible at the next update of the process image of the inputs (PIQ) and outputs (PII).

Note
The data consistency set in Step 8 must match the data volume used. If, for example, with a data length of four data words you use a word consistency, this does not ensure that the words are received by the slave in the order in which they were sent by the master. The consistency here is only for individual words. To ensure consistent order of the words, you must use a buffer consistency in this example.

Detailed information about this topic is available in the section entitled "EM 277 PROFIBUS-DP Module Specifications" of the S7-200 system manual in Entry ID: 1109582.

Keywords
Connection, PROFIBUS DP, S7-200, S7-300, EM 277, Variable memory