Toshiba CTX28 manual RBSU/RBSS NT Circuit Pinout on Passive Bus

ISDN Interfaces

RBSU/RBSS Interface Units

modular connectors, as explained in previous paragraphs, maintains control of polarity. The pinout from the RBSU/RBSS circuit to a S-type TE-1 or TA device is shown in Figure 7-18and Table 7-10.

ISDN

	RJ45					RJ45
	Pinout					Pinout
	3					3
RBSU	6					6
NT Circuit
Insert 100-ohm	4					4
TR using RBSU
and RBSS
option switches.	5					5
5434
BRI (four-wire)			3	6	4	5
		S-type, TE-1s or TAs without
		100-ohm terminating resistors
		(maximum eight TE-1s or TAs per
		RBSU/RBSS circuit).

S-type, TE-1 or TA with 100-ohm TR or just a

100-ohm terminating resistor across each pair on a RJ45 jack.

To local

AC Power

Interfaces

To local

AC Power

Figure 7-18 RBSU/RBSS NT Circuit Pinout on Passive Bus

As a parallel bus, the RBSU/RBSS BRI-NT passive bus will accept TE-1 and TA devices scattered on the bus; however, the locations of the TE and TA devices on the S bus is limited by timing considerations. Specifically, the round trip propagation delay of a signal from the RBSU/RBSS circuit to one device must be within four microseconds of the delay from the other device on the bus. That is to say, layer-1 frames from the RBSU/RBSS must be received within a two microsecond window. This says nothing about how large the delay can be. In fact, it can be much larger, as long as the differences remain small.

To control electrical characteristics, a 100-ohm terminating resistor (TR) is required at both ends of the passive bus. One resistor should be across the Tx pair and one across the Rx pair at either end of the passive bus. Branch-type passive bus configurations, shown in Figures 7-19~7-22, may only require a TR on the RBSU/RBSS NT circuit side and not on the TE or TA device side of the bus.

The RBSU and RBSS circuits provide an option switch that allows the 100-ohm TR to be switched into the circuit on the Strata CTX side of the bus (see Table 7-8 on page 7-17and Table 7-11 on page 7-22). Most TE-1 and TA devices also provide option switches to connect 100-ohm terminating resistors as shown in Figure 7-17.

If the TE or TA devices do not provide TRs, they may be permanently wired in place on a RJ45 jack at the far end of the bus. Only one terminating resistor on each pair should be on the far (TE) end of the passive bus - do not switch in TRs on more than one TE-1 or TA device on the passive bus.

Important! The correct placement of TRs on the Passive Bus is critical to ISDN BRI circuit operation (see the following RBSU/RBSS Passive Bus configurations section).

Strata CTX I&M 06/04 7-25