Appendix A.
MODBUS RTU/RS485
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.
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
and
MODBUS over serial line specification and
implementation guide V1.02
.
NOTE:
The above referenced specifications are available
from the modbus organization at
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:
– Vendor name
– 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.
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Summary of Contents for Panametrics Aurora H2O
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