Strange behaviour for an S7 counter?

[uptown47]

Hi all,

I was messing around with a counter today, using the Set and Preset Value inputs. I would normally post a picture of the code but, as I haven't got S7 on this computer, I'll just describe the 2 lines of ladder and the unusual outcome I experienced to see if anyone has an explaination...

Network 1:
If I0.0 comes on MOVE 8 into MW20

Network 2:
A Counter with I0.1 on the SET input and MW20 on the PRESET VALUE input.

Behaviour:
Switch I0.0 on and MW20 is equal to 8

Switch I0.1 on and 8 goes into the counter

All fine

Change the value to 10 and do the same, PLC goes to STOP mode
Same behaviour with values 11,12,13,14,15 (i.e. all the HEX letters).

When the value is 16, the counter works again

This is something to do with values that are represented with letters in HEX.

I had the same problem with 170 (i.e. AA) but not with 60 (i.e 96)

???

Anyone any ideas why this might be??

 

[L D[AR2P#0.0]]

Count values are in BCD and go from 0 to 999

A count of 10(decimal) is entered as 10(hexadecimal)=16 (decimal)

An invalid count value (i.e. not a bcd number) results in an error OB being called.

 

[L D[AR2P#0.0]]

Example use of int to bcd:

 

[uptown47]

Simon,

Thanks a million for that!

That explains it all brilliantly.

Many thanks for clearing that up.

Cheers

;-)