Modicon Driver problem


Thread Starter

Rodney Hackney

I am currently working on a project that uses a Control Microsystems PLC (which uses Modbus protocol) and a Eaton IDT Panelmate HMI unit. My problem is that when I try to scale the analog data in the Panelmate, I lose part of the data. The range is 0-32760 and I only get 4 digits. If the current value in the plc is 23345 my diplay gets 3345.

The Panelmate Modicon Driver is for Modbus RTU or ASCII modes and lets you select from the type of Modicon PLC you are connecting to 484,585,885,985 or Quantum. If anyone has any suggestions please advise.

There are only 4 significant digits available from a 12 bit AtoD converter, so an engineering quantity like 23345 gpm is bogus. The correct value is 23340 because you have no way to measure
the last digit. What I do in this situation is place the 2334 on the screen with a link to the PLC address and place a 0 at the end of the number as part of the screen background.

Jay Kirsch
Macro Automatics
2985 E. Hillcrest Drive, Ste 101
Thousand Oaks, CA 91362
[email protected]
I cheat and write this in two sets of code or two words. Is the last device only using a 16 bit processor? We got around this using custom code and scaling on those type of machines that read 4xxxx registers in BCD (4 numbers,16 bit). Try sending 20000 (actually 2 decimal) in the first word and 3345 in the second one. If the graphics lets you display them close enough the user won't know the difference.

R A Peterson

many people implement the modbus protocal so that integers can only be numbers from 0-9999, in the mistaken belief that there is some inherent limit
set in modbus for this. there is not but i have seen this done in several modbus drivers. its a bug that you need to talk with the manufacturer about to get fixed.

i think it must come from the fact that in some modicon products the result of integer math operations overflows at 9999 and only retains the lower four digits.

First try [email protected].
From the top of my head, I guess Panelmate expects analog data not to exceed 9999 counts - as it is usual with MODICON PLC's. The Control Systems PLC probably supports MODBUS correctly, but does not emulate a MODICON PLC correctly in this aspect.
Meir C. Saggie Chief Engineer
AFCON Control and Automation Ltd., P.O.BOX 3120 Petach Tikva, Israel, 49130

T: +972-3-9392404 F: +972-3-9244249 E: <[email protected]>
Hello Rodney,

>The range is 0-32760 and I only get 4
> digits.

I don't know anything about Control Microsystem PLC's but;

I wonder if your Control Microsystems PLC is taking your 15 bit integer value and converting it to a 4 digit BCD value (dropping the most sig. digit somehow) and then presenting that value to a 4XXXX address so that it can be read by a Modbus driver and your Panelmate.

I would suggest that you try to view the actual data in the PLC that is in the 4XXXX address. I quess what I am saying is that your problem may be in the PLC where the data is mapped from a Control MicroSystems memory address format to a Modbus format.

Let me know if this helps.

Bradley G. Hite
Intertech Inc.
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