mc68hc908mr24 Freescale Semiconductor, Inc, mc68hc908mr24 Datasheet - Page 358

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

Analog-to-Digital Converter (ADC)
19.4.2 Voltage Conversion
19.4.3 Conversion Time
Advance Information
358
NOTE:
NOTE:
When the input voltage to the ADC equals V
signal to $3FF (full scale). If the input voltage equals V
converts it to $000. Input voltages between V
straight-line linear conversions. All other input voltages will result in
$3FF if greater than V
Input voltage should not exceed the analog supply voltages. See
Analog-to-Digital Converter (ADC)
Conversion starts after a write to the ADSCR. A conversion is between
16 and 17 ADC clock cycles, therefore:
The ADC conversion time is determined by the clock source chosen and
the divide ratio selected. The clock source is either the bus clock or
CGMXCLK and is selectable by ADICLK located in the ADC clock
register. For example, if CGMXCLK is 4 MHz and is selected as the ADC
input clock source, the ADC input clock divide-by-2 prescale is selected
and the bus frequency is 8 MHz:
The ADC frequency must be between f
maximum to meet A/D specifications. See
Converter (ADC)
Since an ADC cycle may be comprised of several bus cycles (four in the
previous example) and the start of a conversion is initiated by a bus cycle
write to the ADSCR, from zero to four additional bus cycles may occur
Number of bus cycles = conversion time x bus frequency
Number of bus cycles = 8 s x 8 MHz = 64 to 68 cycles
Analog-to-Digital Converter (ADC)
Conversion time =
Conversion time =
Characteristics.
REFH
and $000 if less than V
16 to17 ADC cycles
16 to17 ADC cycles
ADC frequency
Characteristics.
4 MHz/2
ADIC
21.14 Analog-to-Digital
REFH
minimum and f
REFH
MC68HC908MR24
, the ADC converts the
Freescale Semiconductor
REFL
and V
= 8 to 8.5 s
REFL
.
REFL
ADIC
, the ADC
are
—
Rev. 4.1
21.14