Siemens SIMATIC S7-200 System Manual page 323

STEP 7- -Micro/WIN Interface
The Modem module allows you to communicate with STEP 7--Micro/WIN over a telephone line
(teleservice). You do not need to configure or program the S7-200 CPU to use the Modem module
as the remote modem when used with STEP 7--Micro/WIN.
Follow these steps to use the Modem module with STEP 7--Micro/WIN:
1. Remove the power from the S7-200 CPU and attach the Modem module to the I/O
expansion bus. Do not attach any I/O modules while the S7-200 CPU is powered up.
2. Connect the telephone line to the Modem module. Use an adapter if necessary.
3. Connect 24 volts DC to the Modem module terminal blocks.
4. Connect the Modem module terminal block ground connection to the system ground.
5. Set the country code switches.
6. Power up the S7-200 CPU and the Modem module.
7. Configure STEP 7--Micro/WIN to communicate to a 10-bit modem.
Modbus RTU Protocol
You can configure the Modem module to respond as a Modbus RTU slave. The Modem module
receives Modbus requests over the modem interface, interprets those requests and transfers data
to or from the CPU. The Modem module then generates a Modbus response and transmits it out
over the modem interface.
Tip
If the Modem module is configured to respond as a Modbus RTU slave, STEP 7--Micro/WIN is
not able to communicate to the Modem module over the telephone line.
The Modem module supports the Modbus functions shown in Table 10-2.
Modbus functions 4 and 16 allow reading or
writing a maximum of 125 holding registers
(250 bytes of V memory) in one request.
Functions 5 and 15 write to the output
image register of the CPU. These values
can be overwritten by user program.
Modbus addresses are normally written as
5 or 6 character values containing the data
type and the offset. The first one or two
characters determine the data type, and the
last four characters select the proper value
within the data type. The Modbus master
device maps the addresses to the correct
Modbus functions.
Creating a Program for the Modem Module
Table 10-2 Modbus Functions Supported by Modem
Module
Function Description
Function 01
Function 02
Function 03
Function 04 Read input (analog input) registers
Function 05
Function 06
Function 15
Function 16
Chapter 10
Read coil (output) status
Read input status
Read holding registers
Write single coil (output)
Preset single register
Write multiple coils (outputs)
Preset multiple registers
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