Siemens SIMATIC S7-200 System Manual page 455

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
PROFIBUS network with a CPU 224 and an EM 277 PROFIBUS--DP module.
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.
Configuration
To use the EM 277 PROFIBUS--DP 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 y
(called a "Send mailbox") which the
master stores in an input area.
Figure A-28 shows an example of the V memory and I/O address area of a PROFIBUS--DP
Master.
The EM 277 PROFIBUS--DP 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.
Figure A-28 shows a memory model of the V memory in a CPU 224 and the I/O address areas of
a DP master CPU. In this example, the DP master has defined an I/O configuration of 16 output
bytes and 16 input bytes, and a V memory offset of 5000. The output buffer and input buffer
lengths in the CPU 224 (determined from the I/O configuration) are both 16 bytes long. The output
data buffer starts at V5000; the input buffer immediately follows the output buffer and begins at
V5016. The output data (from the master) is placed in V memory at V5000. The input data (to the
master) is taken from the V memory at V5016.
g p
Technical Specifications
SIMATIC
S7-300 with
programming
CPU 315-2 DP
device
CPU 400
Figure A-27 EM 277 PROFIBUS- -DP Module and CPU
224 on a PROFIBUS Network
CPU 224
V memory
EM 277
VB0
PROFIBUS- - DP
Module
Offset:
5000 bytes
VB4999
VB5000
Output buffer
(Receive mail-
VB5015
box):16 bytes
VB5016
Input buffer
(Send mailbox):
VB5031
16 bytes
VB5032
VB5119
VB: variable memory byte
Figure A-28 V Memory and I/O Address Area
Appendix A
Figure A-27 shows a
.
ET 200B
EM 277
PROFIBUS--DP
CPU 224
CPU 315-2 DP
I/O address areas
P000
I/O input area:
16 bytes
I/O output area:
16 bytes
P: peripheral
PI: peripheral input
PQ: peripheral output
PI256
PI271
PQ256
PQ271
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