S7-200 Specifications
A-54
S7-200 Programmable Controller System Manual
A5E00066097-02
ET 200B
S7-300 with
CPU 315-2 DP
SIMATIC
programming
device
CPU 400
CPU 224
EM 277 PROFIBUS-DP
Figure A-28 EM 277 PROFIBUS-DP Module and CPU 224 on a PROFIBUS Network
Configuration
To use the EM 277 as a DP slave, you must set the station address of the DP port
to match the address in the configuration of the master. The station address is set
with the rotary switches on the EM 277 module. You must power cycle the CPU
after you have made a switch change in order for the new slave address to take
effect.
The master device exchanges data with each of its slaves by sending information
from its output area to the slave’s output buffer (called a “Receive mailbox”). The
slave responds to the message from the master by returning an input buffer (called
a “Send mailbox”) which the master stores in an input area (see Figure A-29).
The EM 277 can be configured by the DP master to accept output data from the
master and return input data to the master. The output and input data buffers
reside in the variable memory (V memory) of the S7-200 CPU. When you
configure the DP master, you define the byte location in V memory where the
output data buffer should start as part of the parameter assignment information for
the EM 277. You also define the I/O configuration as the amount of output data to
be written to the S7-200 CPU and amount of input data to be returned from the
S7-200 CPU. The EM 277 determines the size of the input and output buffers from
the I/O configuration. The DP master writes the parameter assignment and I/O
configuration information to the EM 277 PROFIBUS DP module. The EM 277 then
transfers the V memory address and input and output data lengths to the S7-200
CPU.
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