Hi,
Depends on your particular needs, here's one way to be used when the value to be added fits within a WORD:
Code:
HW VAR WORD
LW VAR WORD
Temp VAR WORD
AddValue VAR WORD

Temp = LW    ' Copy low word

LW = LW + AddValue

IF LW < Temp THEN   ' Low word wrapped around
  HW = HW + 1
ENDIF
If the value to be added is always one then:
Code:
HW VAR WORD
LW VAR WORD

LW = LW + 1
IF LW = 0 THEN    'Low word wrapped around.
   HW = HW + 1
ENDIF
/Henrik.