Industrial controller with coordinated timing

A method of establishing a coordinated time value among functional modules in an industrial controller, including first functional modules communicating via a first communication link and second functional modules communicating via a second communication link, the first and second communication links connected through a communication module, the modules having internal clocks of predetermined quality, the communication module being in either a local master or dependent state, comprising the steps of:

• (a) for a communication module in a master state:
• (i) receiving from a source functional module a time value on one of the first and second communication links associated with a clock quality;
• (ii) when the associate quality is no less than a stored quality, transmitting the time value on the other of the first and second communication links;
• (iii) when the associated quality is greater than the stored quality, and the time value was received on the first link, changing the communication module to a dependent state;
• (b) for a communication module in the dependent state;
• (i) monitoring the communication link to receive the time value from a source functional module;
• (ii) changing to a local master mode when a monitoring of a communication link indicates a change from the source functional module.

A method of establishing a coordinated time value among functional modules in an industrial controller, including first functional modules communicating via a first communication link and second functional module communicating via a second communication link the first and second communication links connected through a communication module, the second communication link including a master time source, comprising the steps of:

• (a) transmitting a first time value from the master time source on the second communication link;
• (b) receiving at the communication module the time value;
• (c) queueing for transmission of a second time value on the first communication link by the communication module;
• (d) timing the period between step (b) and the availability of the first communication link for transmission of the second time value;
• (e) setting the second time value equal to the first time value plus the period of step (d) and transmitting the second time value on the first communication link.