mc68hc708mp16 Freescale Semiconductor, Inc, mc68hc708mp16 Datasheet - Page 356

• Manufacturer Part Number: mc68hc708mp16
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Analog-to-Digital Converter (ADC)
19.4.1 ADC Port I/O Pins
19.4.2 Voltage Conversion
19.4.3 Conversion Time
Technical Data
356
NOTE:
PTC1/ATD9:PTC0/ATD8 and PTB7/ATD7:PTB0/ATD0 are general-
purpose I/O pins that are shared with the ADC channels.
The channel select bits define which ADC channel/port pin will be used
as the input signal. The ADC overrides the port I/O logic by forcing that
pin as input to the ADC. The remaining ADC channels/port pins are
controlled by the port I/O logic and can be used as general-purpose I/O.
Writes to the port register or DDR will not have any affect on the port pin
that is selected by the ADC. Read of a port pin which is in use by the
ADC will return a logic 0.
When the input voltage to the ADC equals V
signal to $FF (full scale). If the input voltage equals V
converts it to $00. Input voltages between V
line linear conversions. All other input voltages will result in $FF if greater
than V
Input voltage should not exceed the analog supply voltages.
Conversion starts after a write to the ADSCR. Conversion time in terms
of the number of bus cycles is a function of oscillator frequency, bus
frequency, and ADIV prescaler bits. For example, with an oscillator
frequency of 8 MHz, a bus frequency of 4 MHz, and an ADC clock
frequency of 1 MHz, one conversion will take between 16 ADC and 17
ADC clock cycles or between 16 and 17 µs. There will be 128 bus cycles
between each conversion. Sample rate is approximately 30 kHz.
Number of Bus Cycles = Conversion Time x Bus Frequency
DDAD
Analog-to-Digital Converter (ADC)
Conversion Time =
and $00 if less than V
16-17 ADC Cycles
ADC Frequency
SSAD
.
DDAD
DDAD
MC68HC708MP16
and V
, the ADC converts the
Freescale Semiconductor
SSAD,
SSAD
the ADC
are straight-
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Rev. 3.1