EVB20020 Datasheet, PDF (4/5 Pages) SMSC Corporation – Industrial ARCNET AT Adapter Card

USER’S MANUAL FOR EVB-20020 INDUSTRIAL ARCNET ADAPTER CARD
I/O Address Selection
The EVB-20020 is an 8 bit I/O mapped card. The I/O address is selected via DIP switch S1. The switch positions
correspond to address bits A9 – A3. The switch is factory set for address 2E0h. If you encounter problems
accessing the card then you must change the value of the address. To set the address simply set the switch
according the binary representation of that address. For example, address 2E0h would be 1011100. Addresses XX0
– XX7 are used by the network controller and address XX8 selects the Node ID switch.
Node ID Selection
The EVB-20020 is equipped with an on-board Node ID switch mapped at address XX8. The COM20020 network
controller requires a software programmable ID, therefore the switch does not automatically provide a Node ID to the
COM20020. The switch only provides a value to be programmed by the software.
Media Interfaces (Transceivers)
The EVB-20020 supports four types of media interfaces : traditional ARCNET coax and twisted pair line interfaces,
direct coupled RS-485, and isolated RS-485 (twisted pair) ports.
Coaxial Interface
The Coaxial interface uses a standard 93 ohm BNC connector (the same as a 50 ohm BNC) and requires
RG-62 type cable with 93 ohm terminations. The coaxial interface can be used in a bus topology within the
following guidelines:
1. Max. distance 1000′ (without repeaters)
2. Min. distance between nodes 3′
3. Max. number of node per segment 8 (i.e. no repeaters)
4. Max. number of nodes with repeaters 255
Operation is valid only at 2.5 Mbps and uses the SMSC HYC9088 hybrid.
Twisted Pair (TP) Interface
The twisted pair interface utilizes standard 105 ohm 24 AWG unshielded twisted pair cable. The connectors
are RJ-11 modular telephone jacks and follow the ARCNET Trade Association (ATA) standard pinout for
twisted pair with Phase A on pin 3 and Phase B on pin 2. The twisted pair interface can be used in a bus
topology within the following guidelines:
1. Max. distance 400′ (without repeaters)
2. Min. distance between nodes 6′
3. Max. # of nodes 10 (without repeaters)
The line must be terminated at each end of the cable with a 105 ohm impedance resistor. Stubs or
drops are not allowed in the TP interface, cable segments should be connected in a daisy chained fashion.
Note that this TP interface can only be operated at 2.5 Mbps and uses the SMSC HYC9088 hybrid.
Direct Coupled RS-485
The Direct Coupled RS-485 interface uses an RJ-11 connector with Phase A on pin 3 and Phase B on pin 4.
Recommended cable is 24AWG unshielded twisted pair such as Belden #9562. Biasing resistors are
provided (470 ohms) for squelching of reflections. A 75ALS176B transceiver is used. Short stubs or drops
of less than 1 ft. can be accommodated but are not recommended. Data rates from 156 Kbps to 5.0 Mbps
are allowed. Note that the Direct Coupled RS-485 interface is not compatible with either the isolated RS-
485 or the standard ARCNET twisted pair interface.
Isolated RS-485
The Isolated RS-485 interface employs transformer coupling to electrically isolate the data lines and make
the connections insensitive to polarity. Isolation is provided up to 2KV. Data rates from 156 Kbps to 5.0
Mbps are accommodated. Connections are made via pin 2 and 3 of the RJ-11 connectors. Note that the
isolated 485 transceiver utilizes a different modulation technique than the direct coupled scheme and should
not be mixed with direct coupled interfaces or with the standard ARCNET twisted pair interface.
SMSC UG - EVB-20020
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Rev. 1/5/00