Freescale Semiconductor MPC5553, Reference Manual

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MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
19-54 Freescale Semiconductor
• A conversion result. In this case, the stored 16-bit data contains a right justified 14-bit result data.
The conversion result can be calibrated or not depending on the status of CAL bit in the command
that requested the conversion. When the CAL bit is negated, this 14-bit data is obtained by
executing a 2-bit left-shift on the 12-bit data received from the ADC. When the CAL bit is asserted,
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 (See
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
VREF/2 (the msb (most significant bit) 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 .
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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
Bits Name 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.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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
Bits Name 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.