Communications
RS-485 Communications
The QRATE Scanner 3300 supports digital serial communications using EIA-RS-485 hardware with Modicon Modbus
protocol. RS-485 communications are supported by three ports with a baud range of 300 to 115.2K. Ports 1, 2, and 3 can
be used simultaneously, if desired, and all three ports are protected from high-voltage transients. The circuit can be termi
-
nated by enabling an internal termination resistor in the web interface. See the QRATE Scanner 3300 Web Interface User
Manual for details. Wire as shown in
.
Ports 1, 2, and 3 are designed for use with low-power peripherals such as radios, gas chromatographs, other wired Mod
-
bus devices, and wired NUFLO Scanner 2000 series flow computers configured slave devices, and are always enabled. If
a large number of slave devices are to be connected to a QRATE Scanner 3300 network via a serial port, more than one
communication port may be required, depending on archive periods and baud rates desired. The mode (RS-485 or RS-
232) is automatically detected by the hardware.
Note
Not all RS-485 devices, including converters, identify A and B terms consistently. If communications are not
established, switch the wires.
Serial 1, 2 (RS-485)
COM
A
B
RS-485
Device
COM
Serial 3 (RS-232/485)
RS-485
Device
A
B
Figure 3.17 - RS-485 communications
Note
PORT 3 (RS-232/485 3) automatically detects RS-232 and RS-485 based on voltage levels. If RS-232 is being
used, the voltage levels must be valid in order to ensure the port detects RS-232 communication.
RS-232 Communications
Port 3, also supports both RS-232 and RS-485 communications. RS-232 communications are useful for short-range com
-
munications (typically 50 ft or less) with radios and some Modbus peripheral devices. Wire as shown in
COM
CTS
RXD
TXD
RTS
RS-232
Device
Serial 3 (RS-232/485)
Figure 3.18 - RS-232 communications
Note
PORT 3 (RS-232/485 3) automatically detects RS-232 and RS-485 based on voltage levels. If RS-232 is being
used, the voltage levels must be valid in order to ensure the port detects RS-232 communication.
59
QRATE Scanner 3300 integrated control flow computer
Section 3
