I've got a modulo arithmetic question to do with a sensor
outputting data like this:

bits 31-26 ID and parity
bits 25,24,23 modulo counter
bits 22-0 data (LSB bit = 42.91534 micro degrees)

The 3-bit modulo counter increments when crossing from 359 to 0 deg
and decrements when crossing from 0 to 359 deg.

I want  to find the difference between the current reading of the sensor 
and the previous reading.
Using the the least sig bit of the modulo  gives angle polarity but only 
for the rollover between +-360deg.

Here is a table of rollover points as I rotate the sensor a few turns in 
either direction.

DEG/MOD/DATA msb of data
2881  000  0
2879  111  1
2521  111  0
2519  110  1
.
.
1079  010  1
  721  010  0
  719  001  1
  361  001  0
  359  000  1
   +0  000  0
   -0  111  1
-359  111  0
-361  110  1
-719  110  0
-721  101  1
-1079 101  0
.
.
-2519 001  0
-2521 001  1
-2879 000  0
-2881 111  1


Is there some way to get angle polarity  from the modulo at higher 
rollovers, eg 719-721 etc and so work out which way the sensor has 
turned so that after the previous reading has been subtracted from the
current, the difference indicates the angle and direction, of the sensor 
movement.

Thanks for any replies,

Brian Harris






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