Siemens Simatic S7-200 System Manual page 388

S7-200 Programmable Controller System Manual
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 (called a "Send mailbox") which the master buffer (called a "Send mailbox") which the master
stores in an input area.
Figure A-22 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-22 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.
Tip
If you are working with a data unit (consistent data) of three bytes or data units greater than four bytes,
you must use SFC14 to read the inputs of the DP slave and SFC15 to address the outputs of the DP
slave. For more information, see the System Software for S7-300 and S7-400 System and Standard
Functions Reference Manual.
A
376
CPU 224
V memory
EM 277
VB0
Ï Ï Ï Ï
PROFIBUS–DP
Module
Offset:
Ï Ï Ï Ï
5000 bytes
Ï Ï Ï Ï
VB4999
VB5000
Output buffer
Ï Ï Ï Ï
(Receive mail-
VB5015
box):16 bytes
VB5016
Input buffer
(Send mailbox):
Ï Ï Ï Ï
VB5031
16 bytes
VB5032
Ï Ï Ï Ï
VB5119
Ï Ï Ï Ï
VB: variable memory byte
Figure A-22 V Memory and I/O Address Area
CPU 315-2 DP
I/O address areas
P000
PI256
I/O input area:
PI271
16 bytes
PQ256
I/O output area:
16 bytes PQ271
P: peripheral
PI: peripheral input
PQ: peripheral output