Panametrics Aurora H2O, User Manual

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Aurora H2O User’s Manual 7
Appendix A. MODBUS RTU/TCP Communications
Appendix A. MODBUS RTU/TCP Communications
A.1 Introduction
The Aurora H2O supports digital communications using the Modbus/RTU protocol, with 2-wire RS-485 or 3-wire
RS-232C as the physical layer. Data rate can be specified at rates from 4800 to 115200 bits per second (bps), with
selectable parity.
The Aurora H2O supports the Modbus/TCP protocol as defined in: MODBUS Messaging on TCP/IP Implementation
Guide V1.0b.
Aurora H2O has two physically separate communications ports. Both ports can be selected for either RS-232 or
RS-485 operation, and Aurora H2O can communicate with both ports simultaneously.
Note: Aurora H2O supports the Modbus/RTU protocol as defined in:
MODBUS Application Protocol Specification, V1.1b
&
MODBUS over Serial Line Specification and Implementation Guide V1.02.
Note: The above referenced specifications are available from the Modbus Organization at
http://modbus-ida.org.
A.2 Modbus Functions and Data Types
The Modbus functions supported by Aurora H2O include:
• (0x03) Read Holding Registers
• (0x04) Read Input Registers
• (0x08) Diagnostics (Serial Line only) - only supports Echo subcommand
• (0x10) Write Multiple registers
• (0x11) Report Slave ID (Serial Line only)
• (0x2B/0x0E) Read Device Identification - only supports Basic Device Identification tags, which are:
• VendorName
• Product code
• Revision number
Aurora H2O supports data types of Integer and Double/Float. Integer data types are always four (4) bytes long and
should be read with a request for two registers (two bytes per each register, two registers total) at the address.
Double/Float data types provide eight (8) byte double precision data or four (4) byte single precision data,
depending on how many registers are requested. Four registers are used for double data types, and two registers are
used for single precision data types.
Aurora H2O Modbus register addresses are zero-based . Certain Modbus master software and devices use
one-based addressing. With such devices, simply add 1 to the register addresses in Table 7 on page 12 for correct
operation.