i am collecting data over 4 wire westermo td23 from slave PLCs to a front end PLC. it's a digital microwave system with analogue 4 wire interface cards at voiceband 1200baud. i can collect data for hours or days then the df1 error Message translates to Buffer full. why does it not automatically clear? Most time it does this, but when it does not the plc stops collecting data??

how can i automatically clear the buffer?

Grant

Tele Greenland

 

I cannot answer directly and am not sure the exact problem you see. However as background DF1 Full-Duplex includes the TNS (transaction sequence number) and low-end MicroLogix allow up to 4 "pending" transactions" only. Given the ACKs, ENQs, and 3 retries it can take up to 5 (or 10?) minutes for a transaction to abort or fail.

I am gussing that your microwave is NOT returning the responses and you are still issuing new MSG blocks when 4 older "pending transactions" are still ... well, pending.

I would speculate that using ladder logic to manually abort the MSG block would clear the related transaction from the PLC's buffer - however there could be a delay if the "buffer" is waiting for an ACK or NAK. I do not know the timing of this.

But just understand that when you INCREASE the ACK timeout you are committing to wait 3 or 4 times this long for responses. In fact it may be possible that the ACK + retries is STILL going after the MSG block has timed out, but perhaps Rockwell can give a better answer.

best regards
- Lynn A Linse, www.digi.com (Ethernet-to-Serial Experts)

 

Grant,

In your PLC file you should be using a MSG instruction. Directly below the MSG instruction create a new line.

Here is an example: BST XIC MG11:0/DN NXB XIC MG11:0/ER BND OTU MG11:0/EN

You can past this example into the new line. However you will need to change the discrete addresses to match your MSG instruction.

Regards,

Kevin MacMillan