When performing differential measurements, the conversion results can be presented in either a sign/magnitude or two’s complement format.
In sign/magnitude format, the conversion result is a binary representation of the input,
with a sign bit determining the polarity. Figure 1 can be used to calculate the full-scale range of ADC result values
in sign/magnitude format:
n − b i t r a n g e i n s i g n / m a g n i t u d e f o r m a t = ± 2 n − 1 − 1 w h e r e : n = A D C r e s o l u t i o n E x a m p l e s : 12 − b i t A D C = ± 2 12 − 1 − 1 = ± 2047
Figure 1. ADC Range in Sign/Magnitude
Result Format
0x8020’. The 11-bit sign/magnitude formatted result
shows an absolute value of ‘2’ (decimal), with bit 7 of the ADRESH
register representing the sign bit. When the sign bit = ‘0’, the result
is positive, and when the sign bit = ‘1’, the result is negative. For
this example, the sign bit = ‘1’, so the sign/magnitude formatted
decimal result value is ‘-2’.12-Bit Sign/Magnitude Result Format
In two’s complement format, the MSb of the conversion result determines the polarity.
Figure 2 can be used to calculate
the full-scale range of ADC result values in two’s complement format:
n − b i t r a n g e i n t w o ′ s c o m p l e m e n t f o r m a t = ( − 2 n − 1 − 1 ) , ( 2 n − 1 − 2 ) w h e r e : n = A D C r e s o l u t i o n E x a m p l e : 12 − b i t A D C = ( − 2 12 − 1 − 1 ) = − 2047 ( l o w r a n g e ) = ( 2 12 − 1 − 2 ) = 2046 ( h i g h r a n g e )
Figure 2. ADC Range in Two’s Complement
Result Format
0x8020’, which matches
the ADRES result in 12-Bit Sign/Magnitude Result Format. The 12-bit two’s complement result shows a
value of ’-2046’ (decimal), with
bit 7 of the ADRESH register representing the MSb of the conversion result.12-Bit Two’s Complement Result Format
