Delta RMC151 - Manual (Page 565)

6 Communication
Read
Count
(16
bits)
Register
File
(16
bits)
Register
Element
(16
bits)
Description:
Read Count This is the number of 32-bit registers to be read from the
RMC70, starting at the address given by the file and
element.
Register
File
This is the file number of the address of the first register to
be read. For example, for %MD8.12, the file number is 8.
Register
Element
This is the element number of the address of the first
register to be read. For example, for %MD8.12, the
element number is 12.
Receiving the Returned Data
After the write request is sent, the RMC75S will return the requested data. The QJ71C24N
X3 input indicates whether data has been received. To read the receive buffer, use the
GP.BIDIN instruction. The returned data is in the format shown below:
Count
(16
bits)
Data
Item
1
(32
bits)
Data
Item
2
(32
bits)
… Data
Item
n
(32
bits)
Description:
Count This is the number of 32-bit words read from the buffer.
Data Item 1-n This is the returned data.
6.10.4.3. Modbus/RTU Protocol
Modbus/RTU is one of the serial RS-232 and RS-485 protocols supported by the RMC75S. This
topic describes the Modbus/RTU protocol as it applies to the RMC70. For details on configuring
the RMC70 for serial communications, see the Serial Configuration topic.
General
Modbus/RTU is a standard protocol managed by Schneider Automation (Modicon). The
specification is available through Schneider Automation
(http://www.modicon.com/openmbus) and Modbus.org (http://www.modbus.org). The
Modicon Modbus Protocol Reference Guide (PI-MBUS-300) from Modicon is a good
reference for this protocol. It is available through the Modicon web site. At the time of
this writing it was necessary to select the MODBUS/TCP Protocol documents link to find
an Acrobat Reader (.pdf) format version of this document.
RMC70 Support for Modbus/RTU
Modbus, in its various forms such as Modbus/ASCII, Modbus/RTU, Modbus Plus, and
Modbus/TCP, is a request/response protocol. That is, a Modbus master makes a request
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