Analog-to-Digital Converter (ADC)
MCF52211 ColdFire® Integrated Microcontroller Reference Manual, Rev. 2
Freescale Semiconductor 26-37

Figure 26-27. ADC Clock Resynchronization for

Non-Simultaneous Parallel Modes

26.5.10 Voltage Reference Pins VREFH and VREFL

The voltage difference between VREFH and VREFL provides the reference voltage that all analog inputs are

measured against. The reference voltage should be provided from a low noise filtered source capable of

providing up to 1mA of reference current.

Figure 26-28. ADC Voltage Reference Circuit

When tying VREFH to the same potential as VDDA, relative measurements are being made with respect to

the amplitude of VDDA. It is imperative that special precautions be taken to assure the voltage applied to

START0
Asserted
System Clock
Old ADC Clock
ADC Clock After
Resynchronization
ADCA Scan
ADCB Scan
ADCB Scan Start
ADCB Scan Should Start Here
START1 Asserted
ADC Conversion Clock Resynchronized
ADCA Scan Start
Delay in start because ADC Clock cannot
be resynchronized: 5 System Clocks
Wait for next rising
edge of ADC
Conversion Clock
VREFH
External
Reference
Voltage
0.1µF
V
REFL
1.0mH
VRL
SEL_VREFL
VREFH to ADC
VREFL to ADC
SEL_VREFH
VRH