Chapter 23 Analog-to-Digital Converter (ADC)
MPC5602P Microcontroller Reference Manual, Rev. 4
Freescale Semiconductor
585
Figure 23-4. Prescaler simplified block diagram
The clock stretching is implemented if and only if ADCLKSEL = 0 (and clock is half of the
MC_PLL_CLK).
23.3.3
ADC sampling and conversion timing
In order to support different loading and switching times, several different Conversion Timing registers
(CTR) are present. There is one register per channel type. INPLATCH and INPCMP configurations are
limited when the system clock frequency is greater than 20 MHz.
When a conversion is started, the ADC connects the internal sampling capacitor to the respective analog
input pin, allowing the capacitance to charge up to the input voltage value. The time to load the capacitor
is referred to as sampling time. After completion of the sampling phase, the evaluation phase starts and all
the bits corresponding to the resolution of the ADC are estimated to provide the conversion result.
The conversion times are programmed via the bit fields of the CTR. Bit fields INPLATCH, INPCMP, and
INPSAMP define the total conversion duration (T
conv
) and in particular the partition between sampling
phase duration (T
sample
) and total evaluation phase duration (T
eval
).
23.3.3.1
ADC_0
represents the sampling and conversion sequence.
CTU trigger signal
ADCClk
MC_PLL_CLK
Clock
Prescaler
CTU trigger signal
MC_PLL_CLK
ADCClk
MC_PLL_CLK
ADCClk
CTU trigger signal
ADCLKSEL
MC_PLL_CLK
MC_PLL_CLK/2
ADCLKSEL = ‘0’
ADCLKSEL = ‘0’ (clock stretched)
ACKO