s908ey8ad4cfjer Freescale Semiconductor, Inc, s908ey8ad4cfjer Datasheet - Page 49

• Manufacturer Part Number: s908ey8ad4cfjer
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

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:
3.7.1 ADC Status and Control Register
This section describes the function of the ADC status and control register (ADSCR). Writing ADSCR
aborts the current conversion and initiates a new conversion.
COCO — Conversions Complete Bit
Freescale Semiconductor
•
•
•
When AIEN bit is 0, the COCO is a read-only bit which is set each time a conversion is completed
except in the continuous conversion mode where it is set after the first conversion. This bit is cleared
whenever the ADC status and control register is written or whenever the ADC data register is read.
If AIEN bit is 1, the COCO is a read/write bit. Reset clears this bit.
1 = Conversion completed (AIEN = 0)
0 = Conversion not completed (AIEN = 0)/CPU interrupt (AIEN = 1)
ADC status and control register, ADSCR
ADC data registers, ADRH and ARDL
ADC clock register, ADCLK
REFH
Address:
and V
Reset:
Read:
Write:
REFL
$003C
COCO
Figure 3-4. ADC Status and Control Register (ADSCR)
Bit 7
0
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
SSA
SSA
AIEN
6
0
REFH
at the single point ground location.
pin makes a good single point ground location. Connect the V
and V
ADCO
SSA
5
0
REFL
pin. This should be the only ground connection between
REFH
ADCH4
and must be placed as close as possible to the
4
1
and V
ADCH3
REFL
3
1
REFL
loop. The AC current is in the form of
ADCH2
improve ADC performance. 0.01-µF
2
1
ADCH1
1
1
ADCH0
Bit 0
1
I/O Registers
REFL
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