LGB - a control - Fieldbus
The RS485 ring circuit
is the data bus for all of the connected switch, track and special modules. It is a serial bus system, operated in halfduplex mode.A shielded four-conductor phone cable (two twin wires 0.6mm, f.i. J-YSTY) is used for the wiring. Just one of the twin wires is used, the other one is a reserve for future use (in case a second bus becomes necessary).
Starting at the SingleChip-PC the line runs beneath the tracks' route and springs out in those places where modules are needed to operate some function.
Cable type and wiring work
At the right side of the picture: screw terminals for the data line
Connecting the modules
After leading the data cord into a junction box, both of the data wires are connected to each of the modules inside the box. Short T-junctions do the trick to prevent too many efforts. The cable's shield is connected to the modules' common ground. All of the wires are connected to screw terminals. An optocoupler is used to establish a galvanic seperation of the modules.The cable then is led out of the junction box and is looped through the other boxes in the same way, right back to the SingleChip-PC, where a passive terminating resistor is located.
