Appendix B – Drive-to-drive link431Appendix B – Drive-to-drive linkWhat this chapter containsThis chapter describes the wiring of, and available communication methods on thedrive-to-drive link. Examples of using standard function blocks in the communicationare also given starting on page 439.GeneralThe drive-to-drive link is a daisy-chained RS-485 transmission line, constructed byconnecting the X5 terminal blocks of the JCU Control Units of several drives. It isalso possible to use an FMBA Modbus extension module installed into an option sloton the JCU. The firmware supports up to 63 nodes on the link.The link has one master drive; the rest of the drives are followers. By default, themaster broadcasts control commands as well as speed and torque references for allfollowers. The master can also be configured to send a position reference as eithertarget position or synchronization reference. The master can send 8 messages permillisecond at 100/150-microsecond intervals. Sending one message takesapproximately 15 microseconds, which results in a theoretical link capacity ofroughly 6 messages per 100 microseconds.Multicasting the control data and reference 1 to a pre-defined group of drives ispossible, as is chained multicast messaging. Reference 2 is always broadcast by themaster to all followers. See parameters 57.11…57.14.WiringShielded twisted-pair cable (~100 ohm, eg, PROFIBUS-compatible cable) must beused for the wiring. The maximum length of the link is 50 metres (164 ft).The JCU Control Unit has a jumper (J3, “T”) next to the X5 terminal block for bustermination. Termination must be ON on the drives at the ends of the drive-to-drivelink; on intermediate drives, termination must be OFF.Instead of the X5 connector, an FMBA Modbus extension module can be used.For best immunity, high quality cable is recommended. The cable should be kept asshort as possible. Unnecessary loops and running the cable near power cables(such as motor cables) must be avoided.Note: The cable shields are to be grounded to the control cable clamp plate on thedrive. Follow the instructions given in the Hardware Manual of the drive.
