GE GFK-1541B manual Controlling Communications in the Ladder Program

4

Controlling Communications in the Ladder Program

This section provides tips on how to control communications in your ladder program. Only segments of actual ladder logic are included. Topics discussed are:

ƒEssential Elements of the Ladder Program

ƒTroubleshooting Your Ladder Program

ƒMonitoring the Communications Channel

Essential Elements of the Ladder Program

Every ladder program, whether in the developmental phase or the operational phase, should do the following before initiating a COMMREQ function.

1.Initiate the COMMREQ function with a one-shot transitional coil. This prevents sending the same COMMREQ Command Block more than once.

2.Include at least the LAN Interface OK bit in the LAN Interface Status Word as an interlock contact for the COMMREQ function. You may choose to add more interlocks.

3.Zero the word location you specify for the COMMREQ Status (CRS) word and the FT Outputs of the COMMREQ Function Block before the COMMREQ function is initiated.

4.Move the command code and parameters for the Channel command into the memory location specified in IN input of the COMMREQ Function Block before the COMMREQ function is initiated.

The example ladder program segment starting on the next page illustrates how to incorporate these important points in your program.

4-26 TCP/IP Ethernet Communications for the Series 90™ PLC User's Manual– May 2002 GFK-1541B