2-PORT RS-232/422/485 PCI HOST ADAPTER
AT
RT
NE
Figure 3-4. Headers J1B and J2B set for RS-485 “RTS” with “No Echo.”
AT
RT
NE
Figure 3-5. Headers J1B and J2B set for RS-485 “RTS” with “Echo.”
3.2 Address and IRQ selection
The Adapter is automatically assigned I/O addresses and IRQs by your motherboard BIOS. Only the I/O address may be modified by the user.
Adding or removing other hardware may change the assignment of I/O addresses and IRQs.
3.3 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 1K ohm pull-up/pull-down combination that biases the receiver inputs. Headers J1A and J2A allow the user to customize this interface to their specific requirements. Each jumper position corresponds to a specific portion of the interface. If multiple Adapters are configured in a RS-485 network, only the boards on each end should have jumpers T, P & P ON. Refer to the following table for each position’s operation:
