Modes Of Operation; Starting A Conversion - Silicon Laboratories C8051F300 Manual

5.3.

Modes of Operation

ADC0 has a maximum conversion speed of 500 ksps. The ADC0 conversion clock is a divided version of
the system clock, determined by the AD0SC bits in the ADC0CF register (system clock divided by
(AD0SC + 1) for 0 ≤ AD0SC ≤ 31).

5.3.1. Starting a Conversion

A conversion can be initiated in one of five ways, depending on the programmed states of the ADC0 Start
of Conversion Mode bits (AD0CM2–0) in register ADC0CN. Conversions may be initiated by one of the fol-
lowing:
1. Writing a '1' to the AD0BUSY bit of register ADC0CN
2. A Timer 0 overflow (i.e. timed continuous conversions)
3. A Timer 2 overflow
4. A Timer 1 overflow
5. A rising edge on the CNVSTR input signal (pin P0.6)
Writing a '1' to AD0BUSY provides software control of ADC0 whereby conversions are performed "on-
demand". During conversion, the AD0BUSY bit is set to logic 1 and reset to logic 0 when the conversion is
complete. The falling edge of AD0BUSY triggers an interrupt (when enabled) and sets the ADC0 interrupt
flag (AD0INT). Note: When polling for ADC conversion completions, the ADC0 interrupt flag (AD0INT)
should be used. Converted data is available in the ADC0 data register, ADC0, when bit AD0INT is logic 1.
Note that when Timer 2 overflows are used as the conversion source, Timer 2 Low Byte overflows are
used if Timer 2 is in 8-bit mode; Timer 2 High byte overflows are used if Timer 2 is in 16-bit mode. See
tion "15. Timers" on page 143
Important Note About Using CNVSTR: The CNVSTR input pin also functions as Port pin P0.6. When the
CNVSTR input is used as the ADC0 conversion source, Port pin P0.6 should be skipped by the Digital
Crossbar. To configure the Crossbar to skip P0.6, set to '1' Bit6 in register XBR0. See
Input/Output" on page 103
for timer configuration.
for details on Port I/O configuration.
Rev. 2.9
C8051F300/1/2/3/4/5
Section "12. Port
Sec-
39