UM10375 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
User manual Rev. 3 — 14 June 2011 314 of 368
NXP Semiconductors
UM10375
Chapter 20: LPC13xx Analog-to-Digital Converter (ADC)
20.6.1 A/D Control Register (AD0CR - 0x4001 C000)
The A/D Control Register provides bits to select A/D channels to be converted, A/D timing,
A/D modes, and the A/D start trigger.
Table 305: A/D Control Register (AD0CR - address 0x4001 C000) bit description
Bit Symbol Value Description Reset
Value
7:0 SEL Selects which of the AD7:0 pins is (are) to be sampled and converted. Bit 0 selects Pin
AD0, bit 1 selects pin AD1,..., and bit 7 selects pin AD7.
In software-controlled mode (BURST = 0), only one channel can be selected, i.e. only one
of these bits should be 1.
In hardware scan mode (BURST = 1), any numbers of channels can be selected, i.e any
or all bits can be set to 1. If all bits are set to 0, channel 0 is selected automatically (SEL =
0x01).
0x00
15:8 CLKDIV The APB clock (PCLK) is divided by CLKDIV +1 to produce the clock for the ADC, which
should be less than or equal to 4.5 MHz. Typically, software should program the smallest
value in this field that yields a clock of 4.5 MHz or slightly less, but in certain cases (such
as a high-impedance analog source) a slower clock may be desirable.
0
16 BURST Burst select 0
0 Software-controlled mode: Conversions are software-controlled and require 11 clocks.
1 Hardware scan mode: The AD converter does repeated conversions at the rate selected
by the CLKS field, scanning (if necessary) through the pins selected by 1s in the SEL
field. The first conversion after the start corresponds to the least-significant bit set to 1 in
the SEL field, then the next higher bits (pins) set to 1 are scanned if applicable. Repeated
conversions can be terminated by clearing this bit, but the conversion in progress when
this bit is cleared will be completed.
Important: START bits must be 000 when BURST = 1 or conversions will not start.
19:17 CLKS This field selects the number of clocks used for each conversion in Burst mode, and the
number of bits of accuracy of the result in the LS bits of ADDR, between 11 clocks
(10 bits) and 4 clocks (3 bits).
000
0x0 11 clocks / 10 bits
0x1 10 clocks / 9 bits
0x2 9 clocks / 8 bits
0x3 8 clocks / 7 bits
0x4 7 clocks / 6 bits
0x5 6 clocks / 5 bits
0x6 5 clocks / 4 bits
0x7 4 clocks / 3 bits
23:20 - Reserved, user software should not write ones to reserved bits. The value read from a
reserved bit is not defined.
NA
26:24 START When the BURST bit is 0, these bits control whether and when an A/D conversion is
started:
0
0x0 No start (this value should be used when clearing PDN to 0).
0x1 Start conversion now.
0x2 Start conversion when the edge selected by bit 27 occurs on
PIO0_2/SSEL/CT16B0_CAP0.
0x3 Start conversion when the edge selected by bit 27 occurs on
PIO1_5/DIR/CT32B0_CAP0.
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