3-36 B30 BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUALDIRECT INPUT AND OUTPUT COMMUNICATIONS CHAPTER 3: INSTALLATION33.4 Direct input and output communications3.4.1 DescriptionThe direct inputs and outputs feature makes use of the type 7 series of communications modules and allows directmessaging between UR devices. The communications modules are outlined in the table later in this section.The communications channels are normally connected in a ring configuration, as shown in the following figure. Thetransmitter of one module is connected to the receiver of the next module. The transmitter of this second module is thenconnected to the receiver of the next module in the ring. This is continued to form a communications ring. The figureillustrates a ring of four UR-series relays with the following connections: UR1-Tx to UR2-Rx, UR2-Tx to UR3-Rx, UR3-Tx toUR4-Rx, and UR4-Tx to UR1-Rx. A maximum of 16 URs can be connected in a single ring.Figure 3-34: Direct input and output single-channel connectionInter-relay communication (IRC) modules with protocol C37.94 and G.703 are designed for back-to-back communicationconnections, so the ring configuration shown in the previous figure does not apply. To establish inter-relay communicationin more than two URs, you need to have a two-channel IRC module and enable the DIRECT I/O CHANNEL CROSSOVER settingin all relays, as shown in the next figure. This configuration can be expanded to 16 URs, and this configuration does notprovide a redundancy ring since both channels are made into a single ring by the channel crossover function. As per thefigure entitled Typical Pin Interconnection between Two G.703 Interfaces later in this chapter, the clock is supplied typicallyby multiplexer (MUX) and all URs are in Loop Timing Mode. If there is no MUX, then UR1 and UR3 can be in Internal TimingMode and UR2 and UR4 can be in Loop Timing Mode. That is, connected channels must have opposite timing modes.Figure 3-35: Ring configuration for C37.94 module (concept also applies to G.703)The interconnection for dual-channel type 7 communications modules is shown as follows. Two-channel modules allow fora redundant ring configuration. That is, two rings can be created to provide an additional independent data path. Therequired connections are: UR1-Tx1 to UR2-Rx1, UR2-Tx1 to UR3-Rx1, UR3-Tx1 to UR4-Rx1, and UR4-Tx1 to UR1-Rx1 for thefirst ring; and UR1-Tx2 to UR4-Rx2, UR4-Tx2 to UR3-Rx2, UR3-Tx2 to UR2-Rx2, and UR2-Tx2 to UR1-Rx2 for the second ring.
