Microchip SY89468U Bedienungsanleitung


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© 2009 Microchip Technology Inc. DS39705B-page 17-1
10-Bit A/D
Converter
17
Section 17. 10-Bit A/D Converter
HIGHLIGHTS
This section of the manual contains the following major topics:
17.1 Introduction ................................................................................................................. 17-2
17.2 A/D Terminology and Conversion Sequence .............................................................. 17-4
17.3 Registers..................................................................................................................... 17-6
17.4 A/D Module Configuration ......................................................................................... 17-13
17.5 Initialization ............................................................................................................... 17-16
17.6 Controlling the Sampling Process ............................................................................. 17-17
17.7 Controlling the Conversion Process.......................................................................... 17-17
17.8 A/D Results Buffer..................................................................................................... 17-23
17.9 Conversion Sequence Examples.............................................................................. 17-25
17.10 A/D Sampling Requirements..................................................................................... 17-33
17.11 Transfer Function ...................................................................................................... 17-34
17.12 A/D Accuracy/Error ................................................................................................... 17-35
17.13 Operation During Sleep and Idle Modes................................................................... 17-35
17.14 Effects of a Reset...................................................................................................... 17-36
17.15 Register Maps........................................................................................................... 17-37
17.16 Electrical Specifications............................................................................................. 17-38
17.17 Design Tips ............................................................................................................... 17-39
17.18 Related Application Notes......................................................................................... 17-40
17.19 Revision History ........................................................................................................ 17-41
PIC24F Family Reference Manual
DS39705B-page 17-2 © 2009 Microchip Technology Inc.
17.1 INTRODUCTION
The PIC24F 10-bit A/D Converter has the following key features:
• Successive Approximation Register (SAR) Conversion
• Conversion Speeds of up to 500 ksps
• Up to 16 External Analog Input Channels
• Multiple Internal Reference Input Channels (select devices only)
• External Voltage Reference Input Pins
• Unipolar Differential Sample-and-Hold (S/H) Amplifier
• Automatic Channel Scan mode
• Selectable Conversion Trigger Source
• 16-Word Conversion Result Buffer
• Selectable Buffer Fill modes
• Four Options for Results Alignment
• Operation during CPU Sleep and Idle modes
The 10-bit A/D Converter module accepts a single analog signal at any one instant and converts
it to a corresponding 10-bit digital value. It accomodates up to 16 analog inputs and separate ref-
erence inputs; the actual number available on a particular device depends on the package size.
The heart of the module is a Successive Approximation Register (SAR) type of A/D Converter.
Hardware features surrounding the SAR provide flexible configuration and hardware support for
automatic operation, and minimize software overhead, especially in high-speed operation. The
three major sections surrounding the ADC are analog input selection, a memory mapped output
buffer, and timing and control functions.
An internal Sample-and-Hold (S/H) amplifier acquires a sample of an input signal, then holds that
value constant during the conversion process. A combination of input multiplexers selects the
signal to be converted from multiple analog input pins. The whole multiplexer path includes pro-
vision for differential analog input, although the number of negative input pins is limited, and the
signal difference must remain positive (i.e., unipolar). The sampled voltage is held and converted
to a digital value, which strictly speaking, represents the ratio of that input voltage to a reference
voltage. Configuration choices allow connection of an external reference or use of the device
power and ground (AVDD and AVSS). Reference and input signal pins are assigned differently
depending on the particular device.
An array of timing and control selections allow the user to create flexible scanning sequences.
Conversions can be started individually by program control, continuously free running, or triggered
by selected hardware events. A single channel may be repeatedly converted; alternate conver-
sions may be performed on two channels, or any or all of the channels may be sequentially
scanned and converted according to a user-defined bit map. The resulting conversion output is a
10-bit digital number which can be signed or unsigned, left or right justified.
Conversions are automatically stored in a dedicated 16-word buffer, allowing for multiple succes-
sive readings to be taken before software service is needed. Successive conversions are placed
into sequential buffer locations. Alternatively, the buffer can be split into two 8-word sections for
simultaneous conversion and read operations. The module sets its interrupt flag after a selectable
number of conversions, from one to sixteen, when the whole buffer can be read. After the interrupt,
the sequence restarts at the beginning of the buffer. When the interrupt flag is set according to the
earlier selection, scan selections and the Output Buffer Pointer return to their starting positions.
A simplified block diagram for the module is shown in Figure 17-1.
© 2009 Microchip Technology Inc. DS39705B-page 17-3
Section 17. 10-Bit A/D Converter
10-Bit A/D
Converter
17
Figure 17-1: 10-Bit A/D Converter Block Diagram
Comparator
10-Bit SAR Conversion Logic
V +REF
DAC
AN12
AN13
AN14
AN15
AN8
AN9
AN10
AN11
AN4
AN5
AN6
AN7
AN0
AN1
AN2
AN3
V -REF
Sample Control
S/H
AVSS
AVDD
ADC1BUF0:
ADC1BUFF
AD1CON1
AD1CON2
AD1CON3
AD1CHS
AD1PCFG(L)
AD1PCFGH (2)
Control Logic
Data Formatting
Input MUX Control
Conversion Control
Pin Config. Control
Internal Data Bus
16
V +V - RR
MUX AMUX B
VINH
VINL
VINH
VINH
VINL
VINL
VR+
VR-
VR Select
VBG(1)
VBG/2(1)
AD1CSSL
AD1CSSH(2)
Note 1: Internal analog channels are implemented in select devices only. Different device families implement different
combinations of channels. Refer to the specific device data sheet for details.
2: Implemented in select devices only.
CTMU(1)
VDDCORE(1)
AVSS(1)
AVDD(1)


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Modell: SY89468U

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