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16.1 Features
16.2 Description
Basic clocking for the A/D converters is provided by the VPB clock. A programmable
divider is included in each converter, to scale this clock to the 4.5 MHz (max) clock
needed by the successive approximation process. A fully accurate conversion requires 11
of these clocks.
16.3 Pin description
Table 161
Table 161: ADC pin description
Pin
Type
AD0.7:0
Input
&
AD1.7:0
(LPC2134/6/8)
Vref
Reference
V
, V
Power
DDA
SSA
User manual
UM10120
Chapter 16: Analog-to-Digital Converter (ADC)
Rev. 01 — 24 June 2005
•
10 bit successive approximation analog to digital converter (one in LPC2131/2 and
two in LPC2134/6/8).
•
Input multiplexing among 8 pins.
•
Power-down mode.
•
Measurement range 0 to 3 V.
10 bit conversion time ≥ 2.44 µs.
•
•
Burst conversion mode for single or multiple inputs.
•
Optional conversion on transition on input pin or Timer Match signal.
•
Global Start command for both converters (LPC2134/6/8 only).
gives a brief summary of each of ADC related pins.
Description
Analog Inputs. The A/D converter cell can measure the voltage on any of these input
signals. Note that these analog inputs are always connected to their pins, even if the
Pin Multiplexing Register assigns them to port pins. A simple self-test of the A/D
Converter can be done by driving these pins as port outputs.
Note: if the A/D converter is used, signal levels on analog input pins must not be
above the level of V
the A/D converter is not used in an application then the pins associated with A/D
inputs can be used as 5 V tolerant digital IO pins.
Warning: while the ADC pins are specified as 5 V tolerant (see
description" on page
3.3 V (V
) +10 % should not be applied to any pin that is selected as an ADC input,
DDA
or the ADC reading will be incorrect. If for example AD0.0 and AD0.1 are used as the
ADC0 inputs and voltage on AD0.0 = 4.5 V while AD0.1 = 2.5 V, an excessive voltage
on the AD0.0 can cause an incorrect reading of the AD0.1, although the AD0.1 input
voltage is within the right range.
Voltage Reference. This pin is provides a voltage reference level for the A/D
converter(s).
Analog Power and Ground. These should be nominally the same voltages as V
and V
, but should be isolated to minimize noise and error.
SS
Rev. 01 — 24 June 2005
at any time. Otherwise, A/D converter readings will be invalid. If
3A
67), the analog multiplexing in the ADC block is not. More than
User manual
Table 56 "Pin
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
DD
193
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