Section 5. Overview
computers / HMI software, instruments (RTUs) and Modbus-compatible sensors.
The CR800 communicates with Modbus over RS-232, (with a RS-232 to RS-
485 such as an MD485 adapter), and TCP.
Modbus systems consist of a master (PC), RTU / PLC slaves, field instruments
(sensors), and the communication-network hardware. The communication port,
baud rate, data bits, stop bits, and parity are set in the Modbus driver of the master
and / or the slaves. The CR800 supports RTU and ASCII communication modes
on RS-232 and RS485 connections. It exclusively uses the TCP mode on IP
connections.
Field instruments can be queried by the CR800. Because Modbus has a set
command structure, programming the CR800 to get data from field instruments is
much simpler than from serial sensors. Because Modbus uses a common bus and
addresses each node, field instruments are effectively multiplexed to a CR800
without additional hardware.
5.3.5.2 DNP3 — Overview
Related Topics:
• DNP3 — Overview (p. 79)
• DNP3 — Details (p. 436)
The CR800 supports DNP3 slave communications for inclusion in DNP3 SCADA
networks.
5.3.5.3 TCP/IP — Overview
Related Topics:
• TCP/IP — Overview
• TCP/IP — Details
(p. 428)
• TCP/IP Links — List (p. 570)
The following TCP/IP protocols are supported by the CR800 when using network
links
(p. 570) that use the resident IP stack or when using a cell modem with the
PPP/IP key enabled. The following sections include information on some of
these protocols:
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