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Data Highway Description

DH/DH (+); Data Highway/Data Highway (Plus) both developed by Allen Bradley as a [proprietary], industrial bus. The interconnecting cable for the Network Link is called a "Blue Hose" due to the use of Belden 9463 cable [78 ohms, Shielded Twin Axial Cable]. Interconnection between nodes is done over the [Differential LAN] DH, DH+, DH485, or ControlNet Link. DH and DH+ allows 64 nodes, DH485 allows 32, and ControlNet 99 nodes. The protocol used to interconnect the Network link and a PC is called DF1 and provides baseband link for a local area network over RS232 or RS422. Other derivations include; DH+E Link (Plus E), DHIIE Link (IIE), and ControlNet.

DH uses a trunk cable of [up to] 3048 meters, and drop cables [to each node] of 30.48 meters. Uses peer-to-peer communication in which each node [PLC] bids on being the Master, called Floating Master.

DH+ is used with smaller networks. Uses peer-to-peer communication implementing Token passing. Nominal voltages on the bus are 8 to 12 volts p-p; how ever the bus is +/- 200mV sensitive over the 2 differential lines. Each node on the bus is transformer coupled onto the bus. The bus should be terminated to 150 ohms at each end of the bus. Data bits are Manchester encoded [Clock and data are synchronous], and run at 57.6Kb or 115.2Kb [half-duplex]. Each data packet is sent with a 16 bit CRC, or [may also use BCC ~Block check character]. All messages on the bus are either a command or reply.

DH485 is based on EIA-485 and is similar to both DH and DH+. Uses peer-to-peer communication implementing Token passing. It will support up to 32 nodes

RIO [Remote I/O] provides connection between PLC processors [Masters] and I/O adapters [Slaves] and appears to be electrically identical to DH+. However the bus is composed of only one Master and many slaves [1 scanner and 32 adapters]. Nominal voltages on the bus are 8 to 12 volts p-p; how ever the bus is +/- 200mV sensitive over the 2 differential lines. Error checking is done using standard CRC16 checks.
The slave only responds when told to by the master. The link provides transfer of a single unit (8, 16, or 32 bits) of I/O image data to/from each I/O module in each I/O chassis during each I/O scan.

The speed of transmission varies from 57.6 KBps to 230.4 KBps [over a single channel], at distances of 2500 ft to more than 10,000 ft over a 2-wire "Blue Hose" cable [standard PVC twin-axial cable as the transmission medium]. Devices are daisy chained, with half-duplex communication [data passes both ways, but in only one direction at a time. A ½-watt 150 ohm terminating resistor is required at each end of the trunk line to eliminate reflections.

Notes: Belden 9463 cable Multi-Conductor, 1 twinax (2 conductors), 20 AWG, stranded (7x28) TC - Tinned Copper conductors, PE - Polyethylene insulation, Aluminum Foil-Polyester Tape (Beldfoil) shield with a 20 AWG stranded (7x28) tinned copper drain wire and 100% shield coverage plus tinned copper Braid shield with 55% shield coverage, PVC - Polyvinyl Chloride jacket. Used on a 3 pin Phoenix/Euro screw terminal

DF1 refers to the D1 and F1 subset of ANSI /IEEE Standard X3.28 for communications protocol.

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