MC9S08DN60_08 Datasheet, PDF (185/356 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 10 Analog-to-Digital Converter (S08ADC12V1)
Table 10-13. Total Conversion Time vs. Control Conditions
Conversion Type
Subsequent continuous 10-bit or 12-bit;
f_BUS > f_ADCK/11
ADICLK
xx
ADLSMP
1
Max Total Conversion Time
40 ADCK cycles
The maximum total conversion time is determined by the clock source chosen and the divide ratio selected.
The clock source is selectable by the ADICLK bits, and the divide ratio is specified by the ADIV bits. For
example, in 10-bit mode, with the bus clock selected as the input clock source, the input clock divide-by-1
ratio selected, and a bus frequency of 8 MHz, then the conversion time for a single conversion is:
23 ADCK Cyc
Conversion time =
+
8 MHz/1
5 bus Cyc
8 MHz
= 3.5 ms
Number of bus cycles = 3.5 ms x 8 MHz = 28 cycles
NOTE
The ADCK frequency must be between f_ADCK minimum and f_ADCK
maximum to meet ADC specifications.
10.4.5 Automatic Compare Function
The compare function can be configured to check for an upper or lower limit. After the input is sampled
and converted, the result is added to the two’s complement of the compare value (ADCCVH and
ADCCVL). When comparing to an upper limit (ACFGT = 1), if the result is greater-than or equal-to the
compare value, COCO is set. When comparing to a lower limit (ACFGT = 0), if the result is less than the
compare value, COCO is set. The value generated by the addition of the conversion result and the two’s
complement of the compare value is transferred to ADCRH and ADCRL.
Upon completion of a conversion while the compare function is enabled, if the compare condition is not
true, COCO is not set and no data is transferred to the result registers. An ADC interrupt is generated upon
the setting of COCO if the ADC interrupt is enabled (AIEN = 1).
NOTE
The compare function can monitor the voltage on a channel while the MCU
is in wait or stop3 mode. The ADC interrupt wakes the MCU when the
compare condition is met.
10.4.6 MCU Wait Mode Operation
Wait mode is a lower power-consumption standby mode from which recovery is fast because the clock
sources remain active. If a conversion is in progress when the MCU enters wait mode, it continues until
completion. Conversions can be initiated while the MCU is in wait mode by means of the hardware trigger
or if continuous conversions are enabled.
The bus clock, bus clock divided by two, and ADACK are available as conversion clock sources while in
wait mode. The use of ALTCLK as the conversion clock source in wait is dependent on the definition of
MC9S08DN60 Series Data Sheet, Rev 3
Freescale Semiconductor
185