UM10850
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© NXP B.V. 2016. All rights reserved.
User manual
Rev. 2.4 — 13 September 2016
366 of 464
NXP Semiconductors
UM10850
Chapter 25: LPC5410x 12-bit ADC controller (ADC0)
25.6.1 ADC Control Register
This register specifies the clock divider value to be used to generate the ADC clock
in
synchronous mode
and general operating mode bits including resolution and sampling
time.
Table 416. ADC Control Register (CTRL, address offset 0x0) bit description
Bit
Symbol
Value Description
Reset
value
7:0
CLKDIV
In synchronous mode only, the system clock is divided by this value plus one to
produce the clock for the ADC converter, which should be less than or equal to
80 MHz.
Typically, software should program the smallest value in this field that yields this
maximum clock rate or slightly less, but in certain cases (such as a high-impedance
analog source) a slower clock may be desirable.
Remark:
This field is ignored in the asynchronous operating mode.
0
8
ASYNMODE
Select clock mode.
0
0
Synchronous mode. The ADC clock is derived from the system clock based on the
divide value selected in the CLKDIV field. The ADC clock will be started in a controlled
fashion in response to a trigger to eliminate any uncertainty in the launching of an ADC
conversion in response to any synchronous (on-chip) trigger.
In Synchronous mode with the SYNCBYPASS bit (in a sequence control register) set,
sampling of the ADC input and start of conversion will initiate 2 system clocks after the
leading edge of a (synchronous) trigger pulse.
1
Asynchronous mode. The ADC clock is based on the output of the ADC clock divider
ADCCLKSEL in the SYSCON block.
10:9
RESOL
The number of bits of ADC resolution. Accuracy can be reduced to achieve higher
conversion rates. A single conversion (including one conversion in a burst or
sequence) requires the selected number of bits of resolution plus 3 ADC clocks.
Remark:
This field must only be altered when the ADC is fully idle. Changing it during
any kind of ADC operation may have unpredictable results.
Remark:
ADC clock frequencies for various resolutions must not exceed:
- 5x the system clock rate for 12-bit resolution
- 4.3x the system clock rate for 10-bit resolution
- 3.6x the system clock for 8-bit resolution
- 3x the bus clock rate for 6-bit resolution
0
0x0
6-bit resolution. An ADC conversion requires 9 ADC clocks, plus any clocks specified
by the TSAMP field.
0x1
8-bit resolution. An ADC conversion requires 11 ADC clocks, plus any clocks specified
by the TSAMP field.
0x2
10-bit resolution. An ADC conversion requires 13 ADC clocks, plus any clocks
specified by the TSAMP field.
0x3
12-bit resolution. An ADC conversion requires 15 ADC clocks, plus any clocks
specified by the TSAMP field.