GE 90*-30 PLC Series User Manual

Also see for 90-30 PLC: Installation and Hardware Manual

Contents

GFK-1322A Chapter 5 Troubleshooting 5-35Valid BitsEach network variable is assigned a valid bit in the %I reference area associated with eachmodule. For input variables, a ‘1’ in the valid bit location signifies valid data. The bit will becleared to ‘0’ if the data were not updated and the Max Receive Time (if configured to be non-zero) has expired. Thus the PLC logic can determine whether any data is not updated within aspecified time period of time. This can be useful for setting up a “heartbeat” to sense networkintegrity. On power up, the input valid bits are all set to zero until the first update is received.For output network variables, the bit will be cleared if the variable was bound using acknowledgedservice and a message is sent that does not receive acknowledgment. By monitoring the state ofthis bit, the PLC logic can determine whether an output was reliably transmitted.The Valid bits are included in the total length configured in the %I reference area.NoteAn input network variable (a node input) is an output from the LBIM. An outputnetwork variable (a node output) is an input to the LBIM.Input network variables:If the bit is 1: Normal operation.If the bit is 0: The NV has not been updated and the Max Receive Time (if configured to anon-zero value) has expired. This indicates that an input heartbeat has not been received.Output network variables:If the bit is 1: Normal operation.If the bit is 0: The NV has been bound using acknowledged service, the NV was updated,and an Update Failed condition was detected (ACK not received.)Or, The first update has not been sent. (Normal operation during powerup.)Wink FunctionThe LON T ALK wink function is used during network installation to identify unconfigurednodes. If there is more than one unconfigured node on the network, L ON T ALK wink networkmanagement messages can be used to differentiate the nodes.When the LBIM receives a wink message, it responds by flashing the IN MSG and OUTMSG LEDs together five times.