T100MD888 and Maple Systems

[willpower]

Hello, I have an application running with a T100MD888 and a Maple Systems HMI connected via 2 wire RS485.  The HMI is set to the default communication protocol on the PLC.

The communication works well but every once in a while randomly the com light goes out on the HMI, after a second or two it comes back on.  This may happen once or twice or continuiously on and off.

This is somewhat problematic because in this application the plc sends commands to a Delta Systems motion controller that hydraulically positions an indexing setworks bar for a wood edger.  If the operators select a size on the HMI while the com light is out, the plc does not receive the command until the com light goes back on.  If the operator has already fed a piece of lumber into the edger saw and the bar moves, the saw could be damaged badly.

What I need is to solve this problem, what I have found is after system starup the com light usually stays lit for some time, this can be 30 min or 2 hours, it is random.  Once the com light starts to flicker, if I turn the system power off and then on, the problem goes away.

Should I try different communication speeds to get rid of this.  Or can suggest anything else.

Thanks

Will Steed

[support]

Maple System modbus driver does have a tendency to err out once in a while. We find that if you set the Maple HMI comm delay parameter to 0 it works a lot better. Also you may want to try to run a SETPROTOCOL command to fix the RS485 port to RTU protocol only.

It may be better to adjust your system logic a bit so that it must receive the proper parameters before allowing the moving parts to start moving instead of depending on the exact moment for the HMI to send the positional command.

[willpower]

I think I may be ahead of you already, I went through previous posts on the forum and picked up on Setprotocol idea already and have incorporated this into the program prior to posting.  As well as the Maple Systems Comm Delay parameter trick to 0 already.  I still had the same problem.

Could I poll the comm input buffer at a regular interval to stabalize the comm between the PLC and HMI.  I also wonder if I could call a register from the HMI to confirm if the comms are okay to proceed.

Will

[support]

One thing you can try to prevent comm error from affecting the operation is to use the Maple system HMI to turn on an internal relay bit as a flag after it has set the parameter. The PLC will only start the moving sequence when the flag is set. And after the move, the PLC program can clear the flag using the CLRIO command. This way it ensure that a valid paramters is available in the next cycle before it starts cutting.

On communication issue, could you try the following:

1) Use RS232 port instead of RS485 port for the HMI.

2) If using RS485, issue the SETSYSTEM command to make the PLC respond as quickly as possible to incoming command.

3) Try to use bias resistors (560 ohms x 2) to pull up the RS485+ to +9V and RS485- to 0V and see if this helps.

4) Is your PLC program writing to EEPROM regularly? During EEPROM write the interrupt is turned OFF and that can cause lost communication.

5) Ensure that your PLC program does not use any serial port functions such as READMODBUS, WRITEMODBUS, OUTCOMM, PRINT, NETCMD$, READMB2 and WRITEMB2.