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Enhanced Queued Analog-to-Digital Converter (EQADC)
MPC5644A Microcontroller Reference Manual, Rev. 6
1124
Freescale Semiconductor
The ADC conversion speed (in K samples per second - Ksps) is calculated by the following formula. T
he
number of sampling cycles
is determined by the LST bits in the command message - see
Conversion Command Format for the Standard Configuration
” - and it can take one of the following
values: 2, 8, 64, or 128 ADC clock cycles. The
number of AD conversion cycles
is 13 for differential
conversions and 14 for single-ended 12-bit resolution and unitary input gain. The maximum conversion
speed is achieved when the ADC Clock frequency is set to its maximum (15 MHz) and the number of
sampling cycles set to its minimum (2 cycles). The maximum conversion speed for differential and
single-ended conversions are 1Msps and 937.5Ksps, respectively.
shows an example of how the ADC0/1_CLK_PS can be set when using a 120 MHz system
clock and the corresponding conversion speeds for all possible ADC clock frequencies. The table also
shows that according to the system clock frequency, certain clock divide factors are invalid (2, 4, 6, 8 clock
divide factors in the example) since their use would result in a ADC clock frequency higher than the
maximum one supported by the ADC. ADC clock frequency must not exceed 15 MHz.
Table 25-65. ADC Clock Configuration Example (System Clock Frequency=120 MHz)
ADC0/1_CLK_PS [0:4]
ADC0/1_
ODD_PS
System Clock
Divide Factor
ADC Clock
(System Clock =
120 MHz)
Differential
Conversion Speed
with Default
Sampling Time (2
cycles)
Single-Ended
Conversion Speed
with Default
Sampling Time (2
cycles)
0b00000
0
2
N/A
N/A
N/A
1
3
N/A
N/A
N/A
0b00001
0
4
N/A
N/A
N/A
1
5
N/A
N/A
N/A
0b00010
0
6
N/A
N/A
N/A
1
7
N/A
N/A
N/A
0b00011
0
8
15.0 MHz
1.0 Msps
938 Ksps
1
9
13.3 MHz
889 Ksps
833 Ksps
0b00100
0
10
12.0 MHz
800 Ksps
750 Ksps
1
11
10.9 MHz
727 Ksps
682 Ksps
0b00101
0
12
10.0 MHz
667 Ksps
625 Ksps
1
13
9.23 MHz
615 Ksps
577 Ksps
0b00110
0
14
8.57 MHz
571 Ksps
536 Ksps
1
15
8.0 MHz
533 Ksps
500 Ksps
0b00111
0
16
7.5 MHz
500 Ksps
469 Ksps
1
17
7.06 MHz
471 Ksps
441 Ksps
0b01000
0
18
6.67 MHz
444 Ksps
417 Ksps
1
19
6.32 MHz
421 Ksps
395 Ksps
0b01001
0
20
6.0 MHz
400 Ksps
375 Ksps
1
21
5.71 MHz
381 Ksps
357 Ksps
ADCConversionSpeed
ADCClockFrequency MHz
NumberOfSamplingCycles
NumberOfADConversionCycles
+
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
=
Содержание MPC5644A
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