Internet PLC Forum

There can be many possible reasons that lead to communication error.  First of all, make sure that nothing in your program code is writing to the COMM1 port (using statement such as PRINT, OUTCOMM, NETCMD$, READMODBUS or WRITEMODBUS, etc).

Are you using a lot of interrupt based functions in the PLC such as Stepper motor or  high speed counters. When generating high stepping rate or receiving high frequency signal the CPU spend most of its time servicing such task and less time in servicing the RTU. The RTU master may consider that the comm has failed if it did not receive a response within a short period of time. Try to change the timeout value in the HMI if possible. Also try to add time delay between each communication message exchange between the HMI and the PLC.  Also if there is a COMM error, set the HMI to automatically back off for a while before attempting  to communicate again.  Usually the HMI can recover from an occasional COMM error without breaking up with a COMM error message.

You may also want to use the SETPROTOCOL command to set the COMM1 to permanent RTU protocol so that it always respond to MODBUS RTU only.  This may help. However, note that if you use the SETPROTOCOL command then the COMM1 port will not respond to TLServer and you will not be able to use it for programming or on-line monitoring anymore. It will be good to use a special input to SETPROTOCOL the COMM1 back to native mode in order to do programming.

Your PLC need not be connected to the PC that does not have the internet connection. TLServer can be running on any PC in any office LAN as long as the PC is able to access an SMTP server to send emails. . The PLC can be connected to this PC (that has the Internet access) via modems in order to send email. Of course it means that this PC must also have a modem to answer the phone call from the PLC.

Currently, the TLServer does not have the ability to perform the dial-up networking function. Honestly, I am not sure if the O/S will allow an application to quietly dial up the internet on its own and send out data. That sounds like a great security risk to me!

The date and time both have been changed. The reason you don't see it displayed on the LCD is because the "clock.pc5" program loaded in the PLC when it was shipped from factory only displays the date once upon power on reset. It does not keep displaying the date so the LCD doesn't show the new date.

What you need to do is to do an on-line monitoring and click on the "View" button and you will be able to see the new date in the Real Time Clock. You can then click on the "Reset" button and this time the LCD will show the new date.

Note that Interrupt channel #3 corresponds to digital input #6.

INTRDEF 3,2,0 means function #2 will be executed once when input #6 goes from ON to OFF (falling edge).

To pause the whole program, the easiest way is to execute the PAUSE command. But the only way to reset the PLC is to turn OFF the power and ON again, or you have to go to the "On-line monitoring" screen to click on the "Pause" button to clear it.

Another way is to execute the RESET command which will reset the PLC back to its original state when power is first applied to the PLC.

If this is happening to all the LCD, then it appears that the LCD display is affected by switching noise in your panel. It is important to ensure that the LCD cable not be bundled together with high voltage wire in the same conduit. There are  only 5V high impedance signals on the LCD cable and switching of inductive loads on the 24V or 120V wire can impose enough coupled electrincal noise to affect the display.

You may want to shield the LCD cable using some aluminium foil with grounding. Also ensure that you follow good electrical wiring rule by providing flyback diodes or varistor to all solenoid or contactor to snub the inductive back EMF. Although the drivers on the T100MD1616+ has built-in back emf diode to protect itself,  the cables linking the output driver to the load can still induce large enough voltage to affect the LCD display.  

The M-series PLCs do support MODBUS function 05 which is to force set/clear a single output bit. However, your OPC server must support function 05 in order to do so. The bit address in this case can be found in the following link:

http://www.tri-plc.com/appnotes/modbus-map.pdf

This is an updated document of Chapter 5 of the user manual which now include the document on the Bit addressing. To turn ON output 1, execute a Function 05 at address 257.  

Since the LM335 has output of 10mV/K, you can wire up the sensor such that its output voltage fall within the range of the PLC's analog inputs (0-5V for most PLC or 0-1V for 2 of T100MD1616+)  and then you will be able to measure the voltage. The reading obtain is 0-4092 which can be scaled to units you want.

For other interface circuits for LM335, check with NS data sheet:

http://www.national.com/ds.cgi/LM/LM135.pdf