mc68hc908mr24 Freescale Semiconductor, Inc, mc68hc908mr24 Datasheet - Page 363

• Manufacturer Part Number: mc68hc908mr24
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

19.7.6.1 V
19.7.6.2 ANx
19.7.6.3 Grounding
19.8 I/O Registers
MC68HC908MR24 — Rev. 4.1
Freescale Semiconductor
REFH
and V
REFL
Both ac and dc current are drawn through the V
The AC current is in the form of 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 F to 1 F range with good high frequency characteristics. This
capacitor is connected between V
as close as possible to the package pins. Resistance in the path is not
recommended because the dc current will cause a voltage drop which
could result in conversion errors.
Empirical data shows that capacitors from the analog inputs to V
improve ADC performance. 0.01 F and 0.1 F capacitors with good
high-frequency characteristics are sufficient. These capacitors must be
placed as close as possible to the package pins.
In cases where separate power supplies are used for analog and digital
power, the ground connection between these supplies should be at the
V
supplies if possible. The V
location. Connect the V
single point ground location.
These I/O registers control and monitor operation of the ADC:
SSA
•
•
•
pin. This should be the only ground connection between these
ADC status and control register, ADSCR
ADC data registers, ADRH and ARDL
ADC clock register, ADCLK
Analog-to-Digital Converter (ADC)
REFL
SSA
pin to the same potential as V
pin makes a good single point ground
REFH
and V
Analog-to-Digital Converter (ADC)
REFL
REFH
and must be placed
and V
Advance Information
SSAD
REFL
at the
loop.
REFL
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