Using The Em 277 To Connect An S7-200 Cpu To The Network As A Dp Slave - Siemens SIMATIC S7-200 System Manual

Once a DP master has written the parameters and I/O configuration to a DP slave,
and the slave has accepted the parameters and configuration from the master, the
master now owns that slave. The slave only accepts write requests from the
master that owns it. Other masters on the network can read the slave's inputs and
outputs, but they cannot write anything to the slave.

Using the EM 277 to Connect an S7-200 CPU to the Network as a DP Slave

The S7-200 CPU can be connected to a PROFIBUS-DP network through the
EM 277 PROFIBUS-DP expansion slave module. The EM 277 is connected to the
S7-200 CPU through the serial I/O bus. The PROFIBUS network is connected to
the EM 277 PROFIBUS-DP module through its DP communication port. This port
operates at any PROFIBUS baud rate between 9600 baud and 12 Mbaud. (See
Table A-16 for supported baud rates.) As a DP slave device, the EM 277 module
accepts several different I/O configurations from the master to transfer different
amounts of data to and from the master. This feature allows you to tailor the
amount of data transferred to meet the requirements of the application. Unlike
many DP devices, the EM 277 module does not transfer only I/O data. The
EM 277 moves data to and from a block of variable memory defined in the S7-200
CPU. This allows you to exchange any type of data with the master. Inputs,
counter values, timer values, or other calculated values can be transferred to the
master by first moving the data to the variable memory in the S7-200 CPU.
Likewise, data from the master is stored in variable memory in the S7-200 CPU
and can be moved to other data areas.
The DP port of the EM 277 PROFIBUS-DP module can be attached to a DP
master on the network and still communicate as an MPI slave with other master
devices such as SIMATIC programming devices or S7-300/S7-400 CPUs on the
same network.
Figure A-28 shows a PROFIBUS network with a CPU 224 and an EM 277
PROFIBUS-DP module. In this situation, the CPU 315-2 is the DP master and has
been configured by a SIMATIC programming device with STEP 7 programming
software. The CPU 224 is a DP slave owned by the CPU 315-2. The ET 200 I/O
module is also a slave owned by the CPU 315-2. The S7-400 CPU is attached to
the PROFIBUS network and is reading data from the CPU 224 by means of XGET
instructions in the S7-400 CPU user program.
S7-200 Programmable Controller System Manual
A5E00066097-02
S7-200 Specifications
A-53