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Reference, Installation, and Operations Manual Section 2: Product overview
3-9000-743 Rev S June 2013
Communications 35
2.6 Communications
The Daniel Mark III Ultrasonic Gas Flow Meter provides two standard and one optional
RS-232/RS-485 serial communication ports (referred to respectively as Port A, Port B, and Port
C) and an optional Ethernet port (Eth1). Port A and B are expected to be used for (general)
communication with flow computers and RTUs. Port C (included on the Option Board and the
Series 100 Plus Option Board) can be used for general communication (such as with a flow
computer or RTU) or for optional communication as a Modbus master with a Daniel Gas
Chromatograph (GC). With the Series 100 Plus Option Board installed, you can establish
communications with other devices via a Field Communicator (375) or AMS™ Suite). The
Ethernet port is expected to be used for diagnostic purposes. See Section 5.8 for software
configuration of communications protocols.
Port A is the preferred port for connection to a flow computer or RTU. If two flow computers are
to be connected to the meter, then Port B should be used to connect to the second flow
computer. If a computer running the Daniel MeterLink program is to be connected to a meter
and the optional Ethernet port is enabled, it is the preferred port for the connection. If the
Ethernet connection is not feasible, then Daniel MeterLink should be connected to the meter
using Port B in full duplex configuration.
Both Ports A and B are individually hardware-selectable for RS-232/RS-485 Full Duplex/RS-485
Half Duplex operation. Port A supports RS-232 RTS/CTS handshaking with software-configu-
rable RTS on and off delay times. When handshaking is enabled, Port A drives the RTS output
low and expects the CTS input to be active low. Both Ports A and B support individually soft-
ware-configurable transmit delay times.
Port C (provided by the Option Board and the Series 100 Plus Option Board) is individually hard-
ware-selectable for RS-232/RS-485 Half Duplex operation. Port C supports a software-configu-
rable transmit delay time.
Ports A, B, and C support ASCII and RTU Modbus protocols (as detailed in Tab le 2 -1 1) which are
automatically detected on a per-port basis.
Modbus addresses are software configurable (from 1 to 247) on a per-port basis. Ports A and B
operate only as Modbus slaves. Port C can operate as either a Modbus slave (for general
communication) or a Modbus master (for GC communication).
Baud rates are software selectable on a per-port basis from the following:
• ASCII Modbus: 1200, 2400, 9600, 19200, 38400, 57600, 115000 bps
• RTU Modbus: 1200, 2400, 9600, 19200, 38400 bps
Table 2-11 Supported Modbus Protocols
Modbus Protocol Number of Start Bits Number of Data Bits Parity Type Number of Stop Bits
ASCII 1 7 odd or even 1
RTU 1 8 none 1
Daniel MeterLink will not communicate with a Mark III meter over a half-duplex serial
connection.