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Enhanced Queued Analog-to-Digital Converter (EQADC)
MPC5644A Microcontroller Reference Manual, Rev. 6
1138
Freescale Semiconductor
25.6.7.2
External multiplexing
The EQADC can use from one to eight external multiplexer chips to expand the number of analog signals
that may be converted. Up to 64 analog channels can be converted through external multiplexer selection.
The externally multiplexed channels are automatically selected by the CHANNEL_NUMBER field of a
Command Message, in the same way done with internally multiplexed channels. The software selects the
external multiplexed mode by setting the ADC0/1_EMUX bit in either ADC0_CR or ADC1_CR
depending on which ADC will perform the conversion.
shows the channel number
assignments for the multiplexed mode. There are 4 differential pairs, 39 single-ended, and, at most, 64
externally multiplexed channels which can be selected. Only one ADC can have its ADC0/1_EMUX bit
asserted at a time.
INA_ADC0_4
Device Specific
Single-ended
ADC0
1010_0011
163
INA_ADC0_5
Device Specific
Single-ended
ADC0
1010_0100
164
INA_ADC0_6
Device Specific
Single-ended
ADC0
1010_0101
165
INA_ADC0_7
Device Specific
Single-ended
ADC0
1010_0110
166
INA_ADC0_8
Device Specific
Single-ended
ADC0
1010_0111
167
Reserved
1010_1000 to
1100_0001
168 to 193
Reserved
ADC0
1100_0010 to
1100_0111
194 to 199
INA_ADC1_3
Device Specific
Single-ended
ADC1
1100_0010
194
INA_ADC1_4
Device Specific
Single-ended
ADC1
1100_0011
195
INA_ADC1_5
Device Specific
Single-ended
ADC1
1100_0100
196
INA_ADC1_6
Device Specific
Single-ended
ADC1
1100_0101
197
INA_ADC1_7
Device Specific
Single-ended
ADC1
1100_0110
198
INA_ADC1_8
Device Specific
Single-ended
ADC1
1100_0111
199
Reserved
1100_1000 to
1101_1111
200 to 223
Reserved
1110_0xxx to 1111_1xxx
224 to 255
1
The two on-chip ADCs can access the same analog input pins but simultaneous conversions are not allowed. Also,
when one ADC is performing a differential conversion on a pair of pins, the other ADC must not access either of
these two pins as single-ended channels.
2
Old version has reserved values for channel numbers 8 to 11 when EMUX =1. Therefore, now the behavior is
different because it is converted the signal at AN8 to AN11, respectively.
3
VREF=VRH-VRL.
4
50% x VREF = 50% ref = (VRH / VRL)/2, but this only applies before calibration. After calibration, the 50% reference
point will actually return approximately 20 mV lower than the expected 50% of the difference between the High
Reference Voltage (VRH) and the Low Reference Voltage (VRL). For calibration of the ADC only the 25% and 75%
points should be used as described in
Section 25.7.6, ADC Result Calibration
.
Table 25-70. Multiplexed Channel Assignments
1
(continued)
Input Pins
ADC
Channel Number in
CHANNEL_NUMBER Field
Содержание MPC5644A
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