LPC2917_19_1 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 01 — 31 July 2008 34 of 67
NXP Semiconductors
LPC2917/19
ARM9 microcontroller with CAN and LIN
• CLK_SYS_MSCSS_A clocks the AHB side of the AHB-to-APB bus bridge
• CLK_MSCSS_APB clocks the subsystem APB bus
• CLK_MSCSS_MTMR0/1 clocks the timers
• CLK_MSCSS_PWM0..3 clocks the PWMs.
Each ADC has two clock areas; a APB part clocked by CLK_MSCSS_ADCx_APB (x = 1
or 2) and a control part for the analog section clocked by CLK_ADCx = 1 or 2), see
Section 7.2.2.
All clocks are derived from the BASE_MSCSS_CLK, except for CLK_SYS_MSCSS_A
which is derived form BASE_SYS_CLK, and the CLK_ADCx clocks which are derived
from BASE_CLK_ADC. If specific PWM or ADC modules are not used their corresponding
clocks can be switched off.
8.7.5 Analog-to-digital converter
8.7.5.1 Overview
The MSCSS in the LPC2917/19 includes two 10-bit successive-approximation
analog-to-digital converters.
The key features of the ADC interface module are:
• ADC1 and ADC2: Eight analog inputs; time-multiplexed; measurement range up to
3.3 V
• External reference-level inputs
• 400 ksample/s at 10-bit resolution up to 1500 ksample/s at 2-bit resolution
• Programmable resolution from 2-bit to 10-bit
• Single analog-to-digital conversion scan mode and continuous analog-to-digital
conversion scan mode
• Optional conversion on transition on external start input, timer capture/match signal,
PWM_sync or ‘previous’ ADC
• Converted digital values are stored in a register for each channel
• Optional compare condition to generate a ‘less than’ or an ‘equal to or greater than’
compare-value indication for each channel
• Power-down mode
8.7.5.2 Description
The ADC block diagram, Figure 9, shows the basic architecture of each ADC. The ADC
functionality is divided into two major parts; one part running on the MSCSS Subsystem
clock, the other on the ADC clock. This split into two clock domains affects the behavior
from a system-level perspective. The actual analog-to-digital conversions take place in the
ADC clock domain, but system control takes place in the system clock domain.
A mechanism is provided to modify configuration of the ADC and control the moment at
which the updated configuration is transferred to the ADC domain.
The ADC clock is limited to 4.5 MHz maximum frequency and should always be lower than
or equal to the system clock frequency. To meet this constraint or to select the desired
lower sampling frequency the clock generation unit provides a programmable fractional
