I am reading an incremental encoder to measure angle. Based on the encoder, I will INC or DEC a word I call "angle" representing the angle in tenths of degrees (3600 = 360 degrees). What I would like to happen is for the angle to switch from -999 to 2600 when decreasing and from 2600 to -999 when increasing.

I thought I could do this, but it only seems to work for increasing. When decreasing, the number just keeps decreasing.

angle VAR Word 
  
 IF angle=2601 THEN
  angle=-999
 ELSEIF angle=-1000 THEN
  angle=2600
 ENDIF 

Clint,
I do not have the answer for you as to why this is not working, but I have learned in using SX SIM on your code is that the compiler is taking your statement of "ELSEIF angle=-1000 THEN" and making it "ELSEIF angle=1000 THEN".  Why the minus value is being made a positive value is something others will need to explain.  I have checked the help file and see no numeric limits for the IF..THEN..ELSEIF..ENDIF  command.

The VIEW LIST of the code for "angle=-1000" is:
  182  0067  0C18        MOV angle_LSB,#(-1000 & 255)   ; angle=-1000
       0068  002D
  183  0069  0CFC        MOV angle_MSB,#(-1000 >> 8)  
       006A  002E
The VIEW LIST for the code of "ELSEIF angle=-1000 THEN" is:
  196  007B  0CE8        CJNE angle_LSB,#1000 & 255,@__ELSE_2
       007C  008D 0743 0010 0A8B
  197  0080  0C03        CJNE angle_MSB,#1000 >> 8,@__ELSE_2
       0081  008E 0743 0010 0A8B
I know someone will be able to help us better understand this.

Clint,
As a workaround, define a CON such as TestLow, giving it a value of -1000.  Then use that CON name in the IF..ENDIF area.  This makes the program function as desired now, but does not explain my earlier observation.

TestLow CON -1000 angle VAR Word
START: 
angle = -1000
MAIN: 
 IF angle = 2601 THEN
     angle = -999
 ELSEIF angle = TestLow THEN
     angle = 2600
 ENDIF

Gary - Thank you very much for giving this your attention. I will give your workaround a try :D For a second there, I thought I'd lost my marbles!

Well that worked okay, but then I realized I need a > or < to take care of situations where the angle skips over the limit (say I go from 2600 to 2610). Now it doesn't work again.

Here's what I'm trying

Clint,
 WORD variables can only hold positive values. When you do a comparison to a negative value, the compiler takes the "two's complient" of the negative value, and uses that. This works fine for "=" and "<>", but it won't work for ">" or "<".

Bean.