A/D Converter - Philips LPC2119 User Manual

Philips Semiconductors
ARM-based Microcontroller

17. A/D CONVERTER

FEATURES
• 10 bit successive approximation analog to digital converter.
• Input multiplexing among 4 pins (LPC2119/2129) or 8 pins (LPC2292/2294)
• Power down mode
• Measurement range 0 to 3 V
• 10 bit conversion time >= 2.44 uS
• Burst conversion mode for single or multiple inputs
• Optional conversion on transition on input pin or Timer Match signal
DESCRIPTION
Basic clocking for the A/D converter is provided by the VPB clock. A programmable divider is included 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.
PIN DESCRIPTIONS
Table 171: A/D Pin Description
Pin Name Type
Ain7:0 Input
V , V Power
3A SSA
REGISTER DESCRIPTION
The base address of the A/D Converter is 0xE003 4000 (page 35). The A/D Converter includes 2 registers as shown in Table
172.
Table 172: A/D Registers
Address
Name
Offset
0 ADCR
0x04 ADDR
A/D Converter
Analog Inputs. The A/D converter cell can measure the voltage on any of these 8 input signals,
but the 64-pin packages restrict the choice to Ain3:0. 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.
Analog Power and Ground. These should be nominally the same voltages as V
but should be isolated to minimize noise and error. The VrefP and VrefN signals of the cell are
internally connected to these pins as well.
A/D Control Register. The ADCR register must be written to select the
operating mode before A/D conversion can occur.
A/D Data Register. This register contains the ADC's DONE bit and (when
DONE is 1) the 10-bit result of the conversion.
Pin Description
Description
204
Preliminary User Manual
LPC2119/2129/2292/2294
and V
3
Access
Read/Write
Read/Write
January 08, 2004
,
SSD