C8051F300/1/2/3/4/5
40
Rev. 2.9
5.3.2. Tracking Modes
According to Table 5.1 on page 47, each ADC0 conversion must be preceded by a minimum tracking time
for the converted result to be accurate. The AD0TM bit in register ADC0CN controls the ADC0 track-and-
hold mode. In its default state, the ADC0 input is continuously tracked except when a conversion is in prog-
ress. When the AD0TM bit is logic 1, ADC0 operates in low-power track-and-hold mode. In this mode,
each conversion is preceded by a tracking period of 3 SAR clocks (after the start-of-conversion signal).
When the CNVSTR signal is used to initiate conversions in low-power tracking mode, ADC0 tracks only
when CNVSTR is low; conversion begins on the rising edge of CNVSTR (see Figure 5.4). Tracking can
also be disabled (shutdown) when the device is in low power standby or sleep modes. Low-power track-
and-hold mode is also useful when AMUX or PGA settings are frequently changed, due to the settling time
requirements described in
Section “5.3.3. Settling Time Requirements” on page 41
.
Figure 5.4. 8-Bit ADC Track and Conversion Example Timing
Write '1' to AD0BUSY,
Timer 0, Timer 2, Timer 1 Overflow
(AD0CM[2:0]=000, 001, 010, 011)
AD0TM=1
Track
Convert
Low Power
Mode
AD0TM=0
Track or
Convert
Convert
Track
Low Power
or Convert
SAR
Clocks
SAR
Clocks
B. ADC Timing for Internal Trigger Source
1
2
3
4
5
6
7
8
9
CNVSTR
(AD0CM[2:0]=1xx)
AD0TM=1
A. ADC Timing for External Trigger Source
SAR Clocks
Track or Convert
Convert
Track
AD0TM=0
Track
Convert
Low Power
Mode
Low Power
or Convert
10
11 12
1
2
3
4
5
6
7
8
9
10
11 12
1
2
3
4
5
6
7
8
9
10
11 12
13
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