RS-422/485 SERIAL INTERFACE PLUS, 4-PORT
Figure 3-9. Headers J1D - J4D, RS-485 “RTS” Enabled, with “Echo.”
3.7 Line Termination
Typically, each end of the RS-485 bus must have line-terminating resistors (RS-422 terminates at the receive end only). A 120-ohm resistor is across each RS-530/422/485 input in addition to a 1-Kohm pull-up/pull-down combination that bias the receiver inputs. Headers J1E through J4E allow the user to customize this interface to their specific requirements. Each jumper position corresponds to a specific portion of the interface. If multiple Serial Interface Plus adapters are configured in a RS-485 network, only the boards on each end should have jumpers T, P, and P ON. Refer to the table on the next page for each position’s operation:
P
P
T
L
L
Figure 3-10. Headers J1E - J4E, Line Termination.
