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Enhanced Queued Analog-to-Digital Converter (EQADC)
MPC5644A Microcontroller Reference Manual, Rev. 6
1130
Freescale Semiconductor
A conversion result is calibrated according to the status of CAL bit in the command that initiated the
conversion. If the CAL bit is asserted, the EQADC will automatically calculate the calibrated result before
sending the result to the appropriate RFIFO or companion module. If the CAL bit is negated, the result is
not calibrated, it bypasses the calibration hardware, and is directly sent to the appropriate RFIFO or
companion module.
25.6.6.7.2
MAC Unit and Operand Data Format
The MAC unit diagram is shown in
. Each on-chip ADC has a separate MAC unit to fine-tune
its conversion results. The description below considers the general calibration constant registers but it is
the same for the alternate calibration constants.
The OCC0/1 operand is a 14-bit signed value stored in the
Section 25.5.3.5, ADC0/1 Offset Calibration
Constant Registers (ADC0_OCCR and ADC1_OCCR)
. The RAW_RES operand is the raw uncalibrated
result, and it is the direct output from the on-chip ADCs but passing through the resolution adjustment
block. The GCC0/1 operand is a 15-bit fixed point unsigned value stored in the
Gain Calibration Constant Registers (ADC0_GCCR and ADC1_GCCR)
GCC_INT.GCC_FRAC
binary format. The integer part of the GCC (GCC_INT=GCC[1]) contains a single
binary digit while its fractional part (GCC_FRAC=GCC[2:15]) contains 14 bits - see
. The
gain constant equivalent decimal value ranges from 0 to 1.999938..., as shown in
. Two is
always added to the MAC output - see
Section 25.7.6.3, Quantization Error Reduction During Calibration
.
CAL_RES output is the calibrated result, and it is a 14-bit unsigned value. CAL_RES is truncated to
0x3FFF, in case of a overflow, and to 0x0000, in case of an underflow.
Figure 25-79. MAC Unit Diagram
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
GCC_INT
GCC_FRAC
GCC[1]
GCC[2:15]
Figure 25-80. Gain Calibration Constant Format
MAC Unit
Calibrated Result (CAL_RES)
(14-bit unsigned value)
Raw Uncalibrated Result
(RAW_RES)
(12-bit unsigned value)
Gain Calibration Constant (GCC0/1)
(15-bit fixed point unsigned value
from ADC0/1_GCCR register)
Offset Calibration Constant (OCC0/1)
(14-bit signed value
from ADC0/1_OCCR register)
+
2
Summary of Contents for MPC5644A
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