Microchip PIC24FJ128GB202 Handleiding

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© 2011 Microchip Technology Inc. DS39739B-page 51-1
12-Bit A
/
D Converter
w/Threshold Detect
51
Section 51. 12-Bit A/D Converter with Threshold Detect
HIGHLIGHTS
This section of the manual contains the following major topics:
51.1 Introduction ................................................................................................................. 51-2
51.2 A/D Terminology and Conversion Sequence .............................................................. 51-4
51.3 Registers ..................................................................................................................... 51-6
51.4 A/D Module Configuration......................................................................................... 51-19
51.5 Initialization ............................................................................................................... 51-23
51.6 Controlling the Sampling Process............................................................................. 51-24
51.7 Controlling the Conversion Process.......................................................................... 51-24
51.8 A/D Results Buffer..................................................................................................... 51-30
51.9 Extended DMA Operations ....................................................................................... 51-34
51.10 Threshold Detect Operation...................................................................................... 51-37
51.11 Conversion Sequence Examples.............................................................................. 51-44
51.12 A/D Sampling Requirements..................................................................................... 51-53
51.13 Transfer Functions .................................................................................................... 51-54
51.14 A/D Accuracy/Error ...................................................................................................51-56
51.15 Operation During Sleep and Idle Modes................................................................... 51-56
51.16 Effects of a Reset ...................................................................................................... 51-57
51.17 Register Maps ........................................................................................................... 51-58
51.18 Electrical Specifications.............................................................................................51-59
51.19 Design Tips ...............................................................................................................51-60
51.20 Related Application Notes......................................................................................... 51-61
51.21 Revision History ........................................................................................................ 51-62
PIC24F Family Reference Manual
DS39739B-page 51-2 © 2011 Microchip Technology Inc.
51.1 INTRODUCTION
The PIC24F 12-bit A/D Converter has the following key features:
• Successive Approximation Register (SAR) Conversion
• Conversion Speeds of up to 200 ksps
• Up to 32 Analog Input Channels (Internal and External)
• Multiple Internal Reference Input Channels
• External Voltage Reference Input Pins
• Unipolar Differential Sample-and-Hold (S/H) Amplifier
• Automated Threshold Scan and Compare Operation to Pre-Evaluate Conversion Results
• Selectable Conversion Trigger Source
• Fixed-Length (one word per channel), Configurable Conversion Result Buffer
• Four Options for Results Alignment
• Configurable Interrupt Generation
• DMA Operation with Indirect Address Generation
• Operation During CPU Sleep and Idle modes
The 12-bit A/D Converter module is an enhanced version of the 10-bit module offered in some
PIC24 devices. Both modules are Successive Approximation Register (SAR) Converters at their
cores, surrounded by a range of hardware features for flexible configuration. This version of the
module extends functionality by providing 12-bit resolution, a wider range of automatic sampling
options, tighter integration with other analog modules, such as the CTMU, and a configurable
results buffer. This module also includes a unique Threshold Detect feature that allows the
module itself to make simple decisions based on the conversion results.
As before, 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 up to 32 analog inputs, both external (analog input pins)
and internal (e.g., on-chip voltage references and other analog modules). The whole multiplexer
path includes provisions for differential analog input, although, with a limited number of negative
input pins. 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. Con-
versions can be started individually by program control, continuously free-running or triggered by
selected hardware events. A single channel may be repeatedly converted. Alternate conversions
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 12-bit digital
number, which can be signed or unsigned, left or right justified. (In some devices, a user-selectable
resolution of 10 bits is available; in other devices, 12-bit resolution is the only option available.)
Conversions are automatically stored in a dedicated buffer, allowing for multiple successive
readings to be taken before software service is needed. The buffer can be configured to function
as a FIFO buffer or as a channel indexed buffer. In FIFO mode, the buffer can be split into two
equal sections for simultaneous conversion and read operations. In Indexed mode, the buffer can
use the Threshold Scan feature to determine if a conversion meets specific, user-defined criteria,
storing or discarding the converted value as appropriate, and then set semaphore flags to
indicate the event. This allows conversions to occur in low-power modes when the CPU is
inactive, waking the device only when specific conditions have occurred.
The module sets its interrupt flag after a selectable number of conversions, when the buffer can be
read, or after a successful Threshold Detect comparison. 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 51-1.
© 2011 Microchip Technology Inc. DS39739B-page 51-3
Section 51. 12-Bit A/D Converter with Threshold Detect
51
12-Bit A
/
D Converter
w/Threshold Detect
Figure 51-1: 12-Bit A/D Converter Block Diagram
Comparator
12-Bit SAR Conversion Logic
VREF+
DAC
AN(n-1)
ANn(1)
AN8
AN9
AN4
AN5
AN6
AN7
AN0
AN1
AN2
AN3
VREF-
Sample Control
S/H
AVSS
AVDD
ADC1BUF0:
ADC1BUFn(3)
AD1CON1
AD1CON2
AD1CON3
AD1CHS
AD1CHITL
AD1CHITH
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 (2)
VBG/6(2)
AD1CSSL
Note 1: Up to 32 analog channels may be implemented, depending on the particular device family and individual device pin
count. Some or all of these may be external channels, depending on the device. Refer to the specific device data
sheet for details.
2: Internal analog channels are implemented with different options in different device families. Refer to the specific
device data sheet for details.
3: The conversion buffer will always be at least the same size (in words) as the number of external channels, rounded
up to the next greater even number. Refer to the specific device data sheet for the exact number.
CTMU(2)
V
DDCORE
(2)
AVSS(2)
AVDD(2)
AD1CON5
VBG/2(2)
VBG
AD1CSSH
AD1CTMENL
AD1CTMENH
AD1DMBUF
AD1CON4

Product specificaties

Merk: Microchip
Categorie: Niet gecategoriseerd
Model: PIC24FJ128GB202

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