I-O Display Systems Basic I/O Product manual Network Type Switch, L1 Repeater, L2 Multidrop

Setup & Installation 2

Network Type Switch:

Based upon the selected network configuration, each BASIC I/O must be setup before communications can begin. This is done with the network switches shown below. The three basic communication connections for individual BASIC I/Os are:

L1 Repeater

Used in RS-422 networks to extend range to5000 feet between units

L2 Multidrop

Used in RS-422 or RS-485 networks. Provides a total network range of 5000 feet.

L3 Last Unit

Must be used in RS-422 and RS-485 networks for the unit most distant from the host

If there is only one BASIC I/O in a network it is designated L3.

For the network layout, the sequential display indicates the letter “L” followed by “1", “2", or “3". As shipped, BASIC I/Os are setup as “l3", Last Unit. This parameter is not changed by push button but is displayed as “l1", “L2", or “L3" after the dip switches have been set and the unit has undergone a power cycle.

When the unit is configured for “L3" a network termination resistor is placed across the differential receiver. A value of 150 Ohms was selected to suit most applications. A detailed analysis of transmission line effects (reflections), which is beyond the scope of this document, would be necessary to select the ideal termination resistor for any given application.

If the customer wishes to terminate the communication bus externally (at the terminal block location) then it is imperative that no BASIC I/O network switches be set to “L3".

EIA standards dictate that the total bus impedance for RS-485 can be no less than 60 Ohms.

2-16(Vol.1)