Micrologix 1500 and 20h fault

Gents,

Did a search for 20h fault and only found problems with 5/04s and no mention of micro's so a litte help here...

Machine: water dispenser
PLC: AB Micrologix 1500, 1764-24BWA and 1764-LRP processor attached via DH-485 to Dell desktop
Input: Accu-sort lazer bar code scanner and Badger scalable flow meter
Output: single solenoid valve, and 3 status lights
In service for ~4 trouble free years

Logic:
Customers scans their card at the reader and the 1500 is fed ASCII from the scanner and crosses with ASCII file uploaded daily from access program on desktop via DH-485. 1500 verifies the customer card is in database and initiates filling sequence, opens solenoid valve, counts gallons, and begins 30 second no-flow timer. Customer pumps water and when no flow is detected when finished pumping, 30 second delay, solenoid valve closes and counter value and customer number sent to desktop to access program for billing.

Problem:
When customer scans card an immediate Major Error S:6 20h fault (PCCC Description: Host has a problem and will not communicate) is set with minor faults of:
S:1/13 1 Major Error Halt
S:5/0 1 Math overflow trap
S:5/15 1 ASCII String Manipulation Error

Got the math overflow figured out with ADD that kissing 32767 to an integer, but the ASCII manipulation problem has got me. Thougths? All ASCII strings used are cleared at the end of each transaction.

Only thing I can figure is the control on the ASCII read was what enabled the ADD that was overflowing...

And I'm assuming that the minor error bits set are what is setting the 20h or?

Any help ya'll could provide would be greatlly appreciated.

Drew

Yeah I know it doesn't mention the micrologix...is it possible that the string is too long?? If they are too long they will set the overflow flag even if they are cleared at the end of each transaction (i think)


You can place an OTU at the end of your ladder logic with the address of S:5/0 to prevent the math overflow trap from occurring...




Do you have the instruction set manual from AB??

Hello!

Let´s check this link,it´s some info about 20h error for math overflow.

http://rockwellautomation.custhelp..../std_adp.php?p_faqid=5269&p_created=880477992

Maybe it could be useful.

Regards.