Cpu Data Transfer Message Format - Siemens SIMATIC S7-200 System Manual

CPU Data Transfer Message Format

A CPU data transfer, either a CPU-to-CPU or a CPU-to-Modbus data transfer, is specified using
the CPU Data Transfer Message Format. A CPU Data Transfer Message is an ASCII string which
can specify any number of data transfers between devices, up to the number of specifications that
fit in the maximum message length of 120 bytes (119 characters plus a length byte). An ASCII
space can be used to separate the data transfer specifications, but is not required. All data
transfer specifications are executed within one connection. Data transfers are executed in the
order defined in the message. If an error is detected in a data transfer, the connection to the
remote device is terminated and subsequent transactions are not processed.
If the operation is specified as a read, Count number of words are read from the remote device
starting at the Remote_address, and then written to V Memory in the local CPU starting at the
Local_address.
If the operation is specified as a write, Count number of words are read from the local CPU
starting at the Local_address, and then written to the remote device starting at Remote_address.
Format: <Operation>=<Count>,<Local_address>,<Remote_address>
The Operation field consists of one ASCII character and defines the type of transfer.
R -- Read data from the remote device
W -- Write data to the remote device
The Count field specifies the number of words to be transferred. The valid range for the count field
is 1 to 100 words.
The Local_address field specifies the V Memory address in the local CPU for the data transfer
(i.e. VW100).
The Remote_address field specifies the address in the remote device for the data transfer (i.e.
VW500). This address is always specified as a V Memory address even if the data transfer is to a
Modbus device. If the remote device is a Modbus device, the conversion between V Memory
address and Modbus address is as follows:
Modbus address = 1 + (V Memory address / 2)
V Memory address = (Modbus address -- 1) * 2
Example: R=20,VW100, VW200 W=50,VW500,VW1000 R=100,VW1000,VW2000
Creating a Program for the Modem Module Chapter 10
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