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Chapter 1
Product Overview
The DH 485 Network
The RS 232C/DF1 Data Link
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The DH-485 communication network allows devices on the plant floor to
share information. Via the network, application programs can:
monitor process and device parameters and status, including fault and
alarm detection
perform data acquisition
perform supervisory control functions
upload/download PLC programs over the network
The DH-485 network offers:
interconnection of up to 32 nodes
multi-master capability
slave devices
token-passing access control
the ability to add or remove nodes without disruption of the network
maximum cable length of 4,000 feet
data rates up to 19,200 baud
The RS-232C/DF1 data link features:
full- or half-duplex DF1 protocol
data rate up to 19,200 baud
cable length up to 50 feet
point-to-point modem connection
Block Check Character (BCC) or Cyclic Redundancy Check (CRC16)
error detection
The DF1 Protocol
DF1 is a full- or half-duplex link protocol designed to carry messages
intact over a link. The link protocol delimits messages, detects and signals
errors, retries after errors and controls message flow.
Full-duplex protocol is intended for high performance applications where
maximum throughput is required. Full-duplex protocol only works on a
point-to-point link that allows for two-way simultaneous transmission.
Half-duplex protocol provides a less effective utilization of resources than
full-duplex, but is easier to implement. It can operate on point-to-point or
multi-point applications.
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