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54
S A G E M E T E R I N G , I N C .
Sage Metering Modbus Protocol
Sage Rio Meters support communication with other
devices via MODBUS® protocol using RTU transmis-
sion mode. The Modbus protocol defines a message
structure that controllers will recognize and use,
regardless of the type of networks over which they
communicate. It establishes a common format for
the layout and contents of message fields.
Transactions use a master-slave technique, in which
only one device (the master) can initiate transactions
(called queries). The other devices (the slaves)
respond by supplying the requested data to the
master and by taking the action requested in the
query. Sage Meters operate as slaves to other Modbus
devices and default to 19200-8-E-1, however, the
following modes may also be software selectable:
9600-8-N-1
(Baud-Bits-Parity-Stop)
9600-8-E-1
9600-8-O-1
1
19200-8-N-1
19200-8-E-1
(Default)
19200-8-O-1
MESSAGE FRAMING
Messages start with a silent interval of at least 3.5
character times followed by 4 fields and then fol-
lowed by another silent interval of at least 3.5 char-
acter times. The first field contains the device
address. The second field contains the function code.
The third field contains the data and byte counts.
The fourth field contains the CRC value.
1 Parity on the Wireless Devices manufactured by Obvius is "None" rather than "Even". The Sage
default is 19200-8-E-1. Change to 19200-8-N-1 for the Obvius Modhoppers and related wireless
devices.
REV. 10-SIX/SRX
O p e r a t i o n s a n d I n s t r u c t i o n M a n u a l
ADDRESS FIELD
The address field contains one byte. Sage Rio Meters
will transmit response packets to addresses which are
between 1 to 240 decimal (inclusive). Modbus packet
writes may be sent to broadcast address 00, however
the Rio will not reply with a response packet.
FUNCTION CODE FIELD
The function code field contains one byte. See the
section titled Function Codes Supported by Sage Rio.
DATA FIELD
The data field contains four or more bytes. This
information is used by the Meter to take the action
defined by the function code, or to read or write data
to one or many registers.
CRC FIELD
The CRC-16 (cyclical redundancy check) field is two
bytes, containing a 16-bit binary value. The CRC
value is calculated by the transmitting device, which
appends the CRC to the message. The receiving
device recalculates a CRC during receipt of the mes-
sage, and compares the calculated value to the actual
value it received in the CRC field. If the two values
are not equal, the message will be discarded.
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