Rev. 1.4 43
C8051F320/1
5.3. Modes of Operation
ADC0 has a maximum conversion speed of 200 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 co
ntinuous conversions)
3. A Timer 2 overflow
4. A Timer 1 overflow
5. A rising edge on the CNVSTR input signal (pin P0.6)
6. A Timer 3 overflow
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 registers, ADC0H:ADC0L, when bit AD0INT
is logic 1. Note that when Timer 2 or Timer 3 overflows are used as the conversion source, Low Byte over-
flows are used if Timer 2/3 is in 8-bit mode; High byte over
flows are used if Timer 2/3 is in 16-bit mode. See
Section “19. Timers” on page 209 for timer configuration.
Important Note About Using CNVSTR: Th
e 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 P0SKIP. See Section “14. Port
Input/Output” on page 126 for details on Port I/O configuration.
