CODA-Series Coriolis mass flow meter operating manual
11
Multidrop Information
CODA devices equipped with an RS-485 interface can operate on
networks with other devices. The CODA RS-485 transceiver is a 1/2 unit-
load transceiver. When deploying CODA devices in an RS-485 network
with multiple types of devices be sure to confirm that the total load of
all devices does not exceed 32 unit loads on an unrepeated network
segment. Consult the EIA-485 standard for more information.
CODA KM-Series devices equipped with an RS-232 interface do not have
a multidrop capable RS-232 transceiver.
If a CODA device is plugged into an RS-232 network with other devices
which have been adapted to support multidrop communication over
RS-232 it will load the bus excessively and prevent other devices from
communicating on that network. This includes other Alicat M-Series,
L-Series, and P-Series devices.
Modbus RTU Serial Protocol
Alicat uses the Modbus standard in which registers are offset by 1 from
addresses, meaning register 1 is equivalent to address 0, but some
systems expect data to be mapped as 0-indexed addresses. Different
Modbus control systems may refer to registers, offsets, or addresses
in their documentation without clarifying their meaning. If your control
system uses a 0-indexed numbering scheme then decrement all register
references in this manual by 1.
If you are unsure of which addressing scheme your control system uses,
perform a test read of register 1200. If the CODA instrument responds with
Error code 2: “Illegal Data Address”, then your system is using the standard
1-indexed numbering system and the values in the manual can be used
as-is. If the device returns a value of 0 instead of an error, decrement all
registers listed in this section by 1 to arrive at the correct offset.
