Section 21. 8-bit A/D Converter

The A/D allows conversion of an analog input signal to a corresponding 8-bit digital number. Theoutput of the sample and hold is the input into the converter, which generates the result via successiveapproximation.
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Section 21. 8-bit A/D ConverterM 21 Convertor 8-bit A/D Section 21. 8-bit A/D Converter HIGHLIGHTS This section of the manual contains the following major topics: 21.1 Introduction ..................................................................................................................21-2 21.2 Control Registers .........................................................................................................21-3 21.3 Operation .....................................................................................................................21-5 21.4 A/D Acquisition Requirements .....................................................................................21-6 21.5 Selecting the A/D Conversion Clock ............................................................................21-8 21.6 Configuring Analog Port Pins.......................................................................................21-9 21.7 A/D Conversions ........................................................................................................21-10 21.8 A/D Operation During Sleep ......................................................................................21-12 21.9 A/D Accuracy/Error ....................................................................................................21-13 21.10 Effects of a RESET ....................................................................................................21-13 21.11 Use of the CCP Trigger ..............................................................................................21-14 21.12 Connection Considerations ........................................................................................21-14 21.13 Transfer Function .......................................................................................................21-14 21.14 Initialization ................................................................................................................21-15 21.15 Design Tips ................................................................................................................21-16 21.16 Related Application Notes..........................................................................................21-17 21.17 Revision History .........................................................................................................21-18 Note: Please refer to Appendix C.3 or device Data Sheet to determine which devices use this module.© 1997 Microchip Technology Inc. DS31021A page 21-1PICmicro MID-RANGE MCU FAMILY21.1 Introduction The analog-to-digital (A/D) converter module has up to eight analog inputs. The A/D allows conversion of an analog input signal to a corresponding 8-bit digital number. The output of the sample and hold is the input into the converter, which generates the result via suc- cessive approximation. The analog reference voltage is software selectable to either the device’s positive supply voltage (VDD) or the voltage level on the VREF pin. The A/D converter has a unique feature of being able to operate while the device is in SLEEP mode. The A/D module has three registers. These registers are: • A/D Result Register (ADRES) • A/D Control Register0 (ADCON0) • A/D Control Register1 (ADCON1) The ADCON0 register, shown in Figure 21-1, controls the operation of the A/D module. The ADCON1 register, shown in Figure 21-2, configures the functions of the port pins. The I/O pins can be configured as analog inputs (one I/O can also be a voltage reference) or as digital I/O. The block diagram of the A/D module is shown in Figure 21-1. Figure 21-1: 8-bit A/D Block Diagram CHS2:CHS0 111 AN7 110 AN6 101 AN5 100 ...