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Section 21. 8-bit A/D Converter

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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 successive approximation. | 21 Microchip Section 21. 8-bit A D Converter HIGHLIGHTS This section of the manual contains the following major topics 8-bit A D Convertor 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 21-1 PICmicro MID-RANGE MCU FAMILY 21.1 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 successive 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 AN7 AN6 AN5 AN4 AN3 VREF AN2 AN1 AN0 PCFG2 PCFG0 Note On some .