Contemporary Controls BASRT-B Installation Manual - Page 11

Browse online or download pdf Installation Manual for Network Router Contemporary Controls BASRT-B. Contemporary Controls BASRT-B 20 pages. Bacnet/ip to ms/tp router

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Operation

MS/TP Port

The MS/TP port uses an isolated EIA-485 transceiver that is

connected to a 3-pin removable connector (Figure 1). The EIA-

485 transceiver's + and – lines tie to + and – pins of the

connector. The SC pin ties to the circuit ground of the EIA-485

transceiver.

In Figure 11 a simplified schematic of the isolated EIA-485

transceiver is shown. Notice that the transceiver common (SC)

is electrically isolated from the router power supply common

(COM) through the use of opto-isolators and an isolated DC-DC

converter. By providing an isolated EIA-485 transceiver there is

less opportunity to damage the transceiver by subjecting it to

high common-mode voltages, but there is still a risk. Surge

suppression is applied between the two differential inputs and

between each input and ground. Since the transceiver is electrically

isolated, the transceiver's circuit common must be brought out

for connection to the other devices on the MS/TP network. This

is accomplished by pin SC. The differential pair is labelled + and –

and corresponds to the same designations in the BACnet MS/TP

standard. This requires a three-wire connection to the MS/TP

network. When connecting other isolated MS/TP devices there

is no problem since each device requires a 3-wire connection.

Just make corresponding connections. For non-isolated MS/TP

devices, usually only a 2-wire connection is provided. The third

wire is the power supply common. In this situation, the SC

connection must be made to the power supply common of the

non-isolated device. Refer to the device vendor's instructions

for connecting such a device.

In a router application where one connection is made to Ethernet

and the other to MS/TP, the location of the router is probably at

the end of the MS/TP bus segment and therefore both bias and

termination must be applied to the segment end. The router is

shipped with bias and termination applied, but this can be changed

by removing three jumpers. This should be done if the router is

to be connected anywhere between the end MS/TP devices.

TD071200-0IC