Communication question

Hi guys

How can one slc5/03 PLC connected in the same DH485 network detect that his slave Micrologix1200 is alive on network. Now I'm sending one message from Micrologix every 10sec to master SLC5/03 and this message resets timer that triggers alarm (loss of communication) if Micrologix receives ER bit for message it knows that loss of comm happened. Is there more clever way to do this without sending message?

Thanks

You Can get the DH485 communication status bits in the Status Files you can use this status to report communication failure

On one of our largest systems, we have a main PLC 5/40E and 6 slc 5/05's
The main and the remote slc's have a timer arrangement that handshakes
if the handshake is missing for a given time it triggers a fault.
Simple but it works!

In addition to the error bit in the MSG block, we read the free running clock in the slave PLCs. If the value doesn't change we start a timer and if it times out we trip an alarm.

Christoph and Tom can explain your idea more detailed. How is this free running clock working and what’s his address? How often do you read FRC? Is a read msg less complex for network than write?



Thanks

Here is the logic. Merry Christmas!

As far as I know reads and writes take the same amount of time to execute.

Praveen is right; the Active Node table is the easiest and quickest method to determine if a node on a DH485 network is communicating.

Status file words S:9 and S:10 hold the Node Status for the DH485 nodes attached to Channel 1 of the SLC-5/03. The status words are different for the Channel 0 serial port (S:67, S:68) and are in the Channel Status (CS0 and CS1) function files on MicroLogix controllers, but they all function the same.

If your MicroLogix is, for example, Node 02, bit number S:9/02 will be =1 when the MicroLogix is connected to the DH485 network.