NXP Semiconductors MPC5566 - Page 857

Enhanced Queued Analog-to-Digital Converter (eQADC)
MPC5566 Microcontroller Reference Manual, Rev. 2
19-54 Freescale Semiconductor
this 14-bit data is the result of the calculations performed in the EQADC MAC unit using the12-bit
data received from the ADC and the calibration constants GCC and OCC (Refer to
Section 19.4.5.4, “ADC Calibration Feature”). Then, this 14-bit data is further formatted into a
16-bit format according to the status of the FMT bit in the conversion command. When FMT is
asserted, the 14-bit result data is reformatted to look as if it was measured against an imaginary
ground at V
REF
/ 2 (the most significant bit (MSB) bit of the 14-bit result is inverted), and is
sign-extended to a 16-bit format as in Figure 19-29. When FMT is negated, the eQADC
zero-extends the 14-bit result data to a 16-bit format as in Figure 19-30. Correspondence between
the analog voltage in a channel and the calculated digital values is shown in Table 19-39.
0123456789101112131415
SIGN_EXT CONVERSION_RESULT (With inverted MSB bit) 0 0
ADC Result
Figure 19-29. ADC Result Format when FMT = 1 (Right Justified Signed)—On-Chip ADC Operation
Table 19-37. ADC Result Format when FMT = 1 Field Descriptions
Field Description
0–1
SIGN_
EXT[0:1]
Sign extension. Only has meaning when FMT is asserted. SIGN_EXT is 0b00 when CONVERSION_RESULT
is positive, and 0b11 when CONVERSION_RESULT is negative.
2–15
CONVERSION
_RESULT
[0:13]
Conversion result. A digital value corresponding to the analog input voltage in a channel when the conversion
command was initiated. The two’s complement representation is used to express negative values.
0123456789101112131415
0 0 CONVERSION_RESULT 0 0
ADC Result
Figure 19-30. ADC Result Format when FMT = 0 (Right Justified Unsigned)—On-Chip ADC Operation
Table 19-38. ADC Result Format when FMT = 0 Field Descriptions
Field Description
0–1
SIGN_
EXT[0:1]
Sign extension. These two bits are always zero for FMT=0 because unsigned results are positive.
2–15
CONVERSION
_RESULT
[0:13]
Conversion result. A digital value corresponding to the analog input voltage in a channel when the conversion
command was initiated.