Master and Slave?

[robert_ 1]

Hi, I've programmed only point to point systems also called direct wiring, but something I've never understood the issue of communications, is the concept of master and slave. What does it mean in words understandable when a device is a master and a slave?. Thaks

[BobB 58]

Master reads and writes - slave responds only but does not instigate reads and writes.

[robert_ 1]

Bobb what you mean read and write? Could you give me an example?

[BobB 58]

Read values from an diesel engine controller, read values from a power monitor, write speed values and start and stop a VSD. Modbus RTU is used for this sort of thing all the time - probably the most common industrial protocol. Modbus can only have 1 master per network and up to 250 odd slaves. Edited 5 Mar 2013 by BobB

[Joe E. 259]

In a nutshell, Master controls the interaction. It schedules communications between itself and the slave (or multiple slaves). The slaves do not control the network and only speak when spoken to.