AC37 High-Speed Communication Adapter Card
AC37: IBM AT TO REMOTE BUS ADAPTER CARD
1-4
RS-485 SERIAL LINE TERMINATION AND BIASING:
The nine jumpers on the AC37 labeled ‘GROUP C’ are used to install transmission line terminators and/or tri-state
biasing resistors as needed. The function of each jumper is as follows:
Jumper C0: Pull-up for TX/RX + line
Jumper C1: Terminator for TX/RX lines
Jumper C2: Pull-down for TX/RX - line
Jumper C3: Pull-up for RX+ line
Jumper C4: Terminator for RX lines
Jumper C5: Pull-down for RX- line
Jumper C6: Pull-up for IRQ + line
Jumper C7: Terminator for IRQ lines
Jumper C8: Pull-down for IRQ - line
Terminating resistors should always be installed at both ENDS of an RS-485 transmission line, and the line must
have only TWO ends. The biasing resistors are only necessary at one place on the line and are typically installed at
the host.
EXAMPLES:
If the AC37 is communicating to a Mistic Model 200 Processor (G4LC32) and is located at one end of the line, install
C1, C3, C5, C6, and C8.
If the AC37 is the host (master) of a Remote I/O Bus and is located at one end of the line, ALL group C jumpers should
be installed.
If the AC37 is to be the host of a Remote I/O Bus and is NOT located at one end of the line, install jumpers C0, C2,
C3, C5, C6, and C8 only. Terminating resistors must be installed at both ends of the transmission lines.
If the AC37 is to be a redundant or passive host which is monitoring a 2-wire Remote I/O link, and is not at one end
of the link, install jumpers on C3 and C5 and remove all other C group jumpers.
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