7
Metretek RS-485 Board Jumper Settings:
A number of jumpers are accessible on the RS-485 board to permit flexibility when
attaching to varied product types in the field. The table below lists the default jumper
settings that will work for most applications. Figure-5 illustrates where these jumpers are
located on the board.
Jumper Default Function
JP 1
In
Enables termination resistor for receiver (RX-A, RX-B), 120 ohms.
JP 2
Out
Enables termination resistor for transmitter (TX-Y TX-Z), 120 ohms.
JP 3
Out
If in, reduces rise & fall times (bandwidth) for data bit transfer.
JP 4
A + B Selects whether transmitter is always enabled (B+C) or controlled by
the DSR signal of the CNI. (A+B)
Table-1
Jumper Assignments
Jumper JP1: When installed, this adds a simple 120 ohm resistive load across the
receiver end of the RS-485 adaptor board. For most applications, this load resistor will
remain installed.
Jumper JP2: When installed, this jumper adds a 120 ohm termination resistor across the
transmitter output. Not often used, the option has been included to address the rare
circumstance where at least two transmitters share the same line, and the length of the
transmission cable ends here. This being the case, it is desirable to terminate the end of
the cable to prevent reflections while the distant transmitter is sending bit streams.
Jumper JP3: When installed, the rise and fall times for each signal transition (slew rate)
are reduced. This might be done for a system having signal integrity problems due to far
end cable reflections, or the need to reduce EMI noise generation. The tradeoff is, of
course, a slower data transfer capability. Default position is not installed.
Jumper JP4: This jumper controls whether the transmitter is continuously enabled, or if it
is only periodically enabled by the CNI microprocessor for transmission bursts. If the
overall system is wired for full-duplex and only the single transmitter element exists, then
it is possible to set the jumper for B+C. If the system is wired for multi-drop with two
transmitters on the same cable, or if it has been wired for half-duplex, then the setting
A+B is mandatory (to prevent line contention).
RS-485 Board Jumper Settings:
A number of jumpers are accessible on the RS-485 board to permit flexibility when
attaching to varied product types in the field. The table below lists the default jumper
settings that will work for most applications. Figure-5 illustrates where these jumpers are
located on the board.
Jumper JP1: When installed, this adds a simple 120 ohm resistive load across the
receiver end of the RS-485 adaptor board. For most applications, this load resistor will
remain installed.
Jumper JP2: When installed, this jumper adds a 120 ohm termination resistor across the
transmitter output. Not often used, the option has been included to address the rare
circumstance where at least two transmitters share the same line, and the length of the
transmission cable ends here. This being the case, it is desirable to terminate the end of
the cable to prevent reflections while the distant transmitter is sending bit streams.
Jumper JP3: When installed, the rise and fall times for each signal transition (slew rate)
are reduced. This might be done for a system having signal integrity problems due to far
end cable reflections, or the need to reduce EMI noise generation. The tradeoff is, of
course, a slower data transfer capability. Default position is not installed.
Jumper JP4: This jumper controls whether the transmitter is continuously enabled, or if it
is only periodically enabled by the CNI microprocessor for transmission bursts. If the
overall system is wired for full-duplex and only the single transmitter element exists, then
it is possible to set the jumper for B+C. If the system is wired for multi-drop with two
transmitters on the same cable, or if it has been wired for half-duplex, then the setting
A+B is mandatory (to prevent line contention).
