Chapter 3: Option Selection; Terminations; Figure 3-1: Simplified Termination Schematic; Data Cable Wiring - IBM LPCI-COM-8SM User Manual

Chapter 3: Option Selection

To help you locate the jumpers described in this section, refer to the Option Selection Map at
the end of this section. Operation of the serial communications section is determined by jumper
installation as described in the following paragraphs.
For the convenience of the user, instructions for the placement of the jumpers is also silk
screened on the back of the card.

Terminations

A transmission line should be terminated at the receiving end in its characteristic impedance.
Installing a jumper at the locations labeled LDxO applies a 120Ω load across the
transmit/receive input/output for RS485 operation.
Jumpers having to do with the termination of each channel are located near the output
connector. They are labeled by channel. The load jumper is labeled "LD". The other two jumpers
are used to connect the transmit and receive lines for the two wire RS485 mode.
In RS485 operations where there are multiple terminals, only the RS485 ports at each end of
the network should have terminating impedance as described above. To so terminate the COM
A port, place a jumper at the location labeled Ch A -LD. To terminate the COM B, COM C, COM
D, COM E, COM F and COM H ports, place jumpers at locations labeled Ch B - LD, Ch C - LD,
Ch D - LD, Ch E - LD, Ch F - LD, Ch G - LD and Ch H - LD respectively.
Also, for RS485 operation, there must be a bias on the TRX+ and TRX- lines. If the card is not
to provide that bias, contact the factory technical support.

Data Cable Wiring

RS-485 Signal Pin Connection
Ain/out+
Ain/out-
100 Ω to Ground

Figure 3-1: Simplified Termination Schematic

2
3
5
Tx+/R x+
LD
120
μ
0.01 F
Tx-/R x-
11 Manual LPCI-COM-8SM