mc68hc908mr32 Freescale Semiconductor, Inc, mc68hc908mr32 Datasheet - Page 51

• Manufacturer Part Number: mc68hc908mr32
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

3.6.5 ADC Voltage In (ADVIN)
ADVIN is the input voltage signal from one of the 10 ADC channels to the ADC module.
3.6.6 ADC External Connections
This section describes the ADC external connections: V
3.6.6.1 V
Both ac and dc current are drawn through the V
current spikes required to supply charge to the capacitor array at each successive approximation step.
The current flows through the internal resistor string. The best external component to meet both these
current demands is a capacitor in the 0.01 µF to 1 µF range with good high frequency characteristics. This
capacitor is connected between V
package pins. Resistance in the path is not recommended because the dc current will cause a voltage
drop which could result in conversion errors.
3.6.6.2 ANx
Empirical data shows that capacitors from the analog inputs to V
and 0.1-µF capacitors with good high-frequency characteristics are sufficient. These capacitors must be
placed as close as possible to the package pins.
3.6.6.3 Grounding
In cases where separate power supplies are used for analog and digital power, the ground connection
between these supplies should be at the V
these supplies if possible. The V
pin to the same potential as V
3.7 I/O Registers
These I/O registers control and monitor operation of the ADC:
Freescale Semiconductor
•
•
•
ADC status and control register, ADSCR
ADC data registers, ADRH and ARDL
ADC clock register, ADCLK
REFH
and V
REFL
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
SSAD
SSA
REFH
at the single point ground location.
pin makes a good single point ground location. Connect the V
and V
SSAD
REFL
REFH
pin. This should be the only ground connection between
and must be placed as close as possible to the
and V
REFH
REFL
and V
REFL
loop. The AC current is in the form of
REFL
improve ADC performance. 0.01-µF
, ANx, and grounding.
I/O Registers
REFL
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