AN840. PIC16F7X/PIC16C7X Peripherals Configuration and Integration INTRODUCTION A/D MODULE CONVERSION BLOCK DIAGRAM

Transcription

1 PIC16F7X/PIC16C7X Peripherals Configuration and Integration Authors: INTRODUCTION In choosing the appropriate microcontroller for a specific application, it is necessary to select one which includes all the needed peripherals. It is also essential to know how to integrate these peripherals to meet the desired output requirements. The PIC16F7X and PIC16C7X families are both 8-bit mid-range microcontrollers. The PIC16F7X family is a Flash device, while the PIC16C7X family is a one-time-programming (OTP) device. Two code examples are presented in this application note covering the Analog-to-Digital Converter (ADC), Timer2, Capture/Compare/PWM (CCP) and the Universal Synchronous Asynchronous Receiver Transmitter (USART), for both the PIC16F7X and PIC16C7X families. This application note covers three main subjects: Configuration of the above-mentioned peripherals Integration of these peripherals How their operation affects the other peripherals Also provided are calculations, data, hardware schematic and source code in C and assembly. A/D MODULE FIGURE 1: AN1 AN0 Mary Tamar Tan, Mark Pallones Microchip Technology Inc. CHS2:CHS0 001 ANALOG-TO-DIGITAL CONVERSION BLOCK DIAGRAM 000 V DD V AIN V REF 8-bit A/D The A/D allows the conversion of an analog input signal to a corresponding 8-bit digital number. The output of the internal sample and hold circuit 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: A/D Control Register 0 (ADCON0) A/D Control Register 1 (ADCON1) A/D Result Register (ADRES) In the sample program (see Appendix A: Source Code in Assembly or Appendix B: Source Code in C ), the code segment, init_adc, sets up the A/D via ADCON0 and ADCON1. The ADCON0 register controls the operation of the A/D module. This register is used to select the conversion clock frequency and the analog channel. It is where the start and completion of conversion is determined. The ADCON1 register configures the functions of the port pins. The PIC16F7X and PIC16C7X microcontrollers have either five or eight I/O pins which can be configured as analog inputs. It is important to take note that ADCON1 does not override the respective TRIS register which is used to configure the data direction of the PORT register. The ADCON1, TRISA and TRISE registers control the operation of the A/D port pins. The port pins that are desired as analog inputs must have their corresponding TRIS bits set (input). The sample programs in Appendix A: Source Code in Assembly and Appendix B: Source Code in C use two analog channels, AN0 and AN1, which are switched after every conversion is completed. After the ADCON0 and ADCON1 registers are configured, the GO/DONE bit in ADCON0 is set to a 1 to start the conversion and then monitored to track when the conversion is complete. When the A/D conversion is complete, the result is loaded into the ADRES register, the GO/DONE bit is cleared, and the A/D Interrupt Flag bit (ADIF) is set. The sample code reads the ADRES register and passes it on to the USART and CCP modules. Switching between the two analog input channels is done by changing the value of the CHS2:CHS0 bits of the ADCON0 register (see Figure 1). Note that Figure 1 only shows AN1 and AN0, but any of the available analog input channels can be selected via the CHS2:CHS0 bits Microchip Technology Inc. DS B-page 1

2 TIMERS The PIC16F7X and PIC16C7X families of devices have three timer modules. Each module can generate an interrupt to indicate that an event has occurred (i.e., timer overflow). The three timer modules are: Timer0 Module Timer1 Module Timer2 Module Timer0 module is a simple 8-bit timer/counter. The clock source can be either the internal system clock (FOSC/4) or an external clock. In Timer mode, the Timer0 module will increment every instruction cycle (without prescaler). In Counter mode, Timer0 will increment, either on every rising or falling edge of pin RA4/T0CKI. Timer1 module is a 16-bit timer/counter consisting of two 8-bit registers (TMR1H and TMR1L), which are readable and writable. The TMR1 register pair (TMR1H:TMR1L) increments from 0000h to FFFFh and rolls over to 0000h. In Timer mode, Timer1 increments every instruction cycle. In Counter mode, it increments on every rising edge of the external clock input. Timer2 is an 8-bit timer with a prescaler, a postscaler and a Period register. Using the prescaler and postscaler at their maximum settings, the overflow time is the same as a 16-bit timer. Timer2 is the PWM time base when the CCP module is used in the PWM mode. Additional information and details on the use of these three timers can be found in the PIC16F7X and PIC16C7X family data sheets. TIMER2 AS THE PWM TIME BASE Timer2 is an 8-bit timer which can be used as the PWM time base for the CCP. For the PWM mode, the following registers need to be configured: Timer2 Period Register (PR2) Timer2 Control Register (T2CON) PIR1 Register The init_timer2 code segment shows an example of the Timer2 configuration for PWM mode (see Appendix A: Source Code in Assembly or Appendix B: Source Code in C ). The PWM output has a time base (period) and a time that the output stays high (duty cycle). The frequency of the PWM is the inverse of the period (1/period). The PWM period is specified by writing to the PR2 register. The PWM duty cycle is latched from CCPR1L into CCPR1H. Setting up the period and duty cycle is discussed in detail in Section PWM Mode of the CCP Module. The TMR2ON bit of the T2CON register is set to start Timer2 operation. The TMR2 register is readable and writable and is cleared on all device Resets. Timer2 increments from 00h until it matches PR2 and then resets to 00h on the next increment cycle. The TMR2 Interrupt Flag bit (TMR2IF) is set whenever a match between the TMR2 and PR2 registers occurs. In the code example, the TMR2IF flag is cleared after every TMR2/PR2 match to reset Timer2 and to signal a start of conversion for the A/D. CAPTURE/COMPARE/PWM MODULE (CCP) PIC16F7X and PIC16C7X have two CCP (Capture/ Compare/PWM) modules. Each module contains a 16-bit register which can operate as a 16-bit Capture register, as a 16-bit Compare register or as a 10-bit PWM Master/Slave Duty Cycle register. The CCP modules are identical in operation, with the exception of the operation of the Special Event Trigger. Each CCP module has three registers, which are shown below: CCP1 CCP2 Comment CCP1CON CCP2CON CCP Control register CCPR1H CCPR2H CCP High byte CCPR1L CCPR2L CCP Low byte CCP1 CCP2 CCP pin Additional information and details on the use of CCP can be found in the PIC16F7X and PIC16C7X family data sheets. DS B-page Microchip Technology Inc.

3 PWM MODE OF THE CCP MODULE Both PIC16F7X and PIC16C7X have two CCP modules that are identical in operation, with the exception being the operation of the Special Event Trigger. In Pulse-Width Modulation (PWM) mode, the CCPx pin produces up to a 10-bit resolution PWM output. Since the CCPx pin is multiplexed with the PORT data latch, the corresponding TRIS bit must be cleared to make the CCPx pin an output. In this application note, only the PWM mode of the CCP2 module is being used. The code example in Appendix A: Source Code in Assembly and Appendix B: Source Code in C sets up the following registers for PWM operation: PORTC Data Direction Register (TRISC) Timer2 Period Register (PR2) CCP2CON Register CCPR2L Register The code segment, init_pwm, is an example on how to initialize the CCP2 module for PWM mode. Since the CCP2 pin is multiplexed with the RC1/CPP2 data latch, the TRISC<1> bit must be cleared to make the CCP1 pin an output. The PWM period is specified by writing to the PR2 register. The PWM period can be calculated using Equation 4. Equation 1 is the formula used to obtain the maximum PWM resolution. Note that the PWM period can also be computed using Equation 4. EQUATION 4: PWM PERIOD EQUATION The PWM frequency (FPWM) is defined as 1 PWM period. For the code example, the Timer2 prescale value is set to 1. TOSC is the reciprocal of the oscillator frequency (FOSC), which is 4 MHz. By equating Equation 3 and Equation 4, expressing TOSC in terms of FOSC and rearranging the terms, the PR2 value can be obtained, as seen in Equation 5 and Equation 6. EQUATION 5: RESULT OF EQUATIONS 3 AND 4 EQUATION 6: PWM Period = PR TOSC (TMR2 Prescale Value) = PR TMR2 prescale value F PWM F OSC PR2 VALUE AS A FUNCTION OF FOSC AND FPWM EQUATION 1: MAXIMUM PWM RESOLUTION EQUATION PR2 F OSC = F PWM 4 TMR2 prescale value 1 A maximum PWM resolution of ten bits is used. To get the value of the PR2 register, the PWM frequency and the PWM period must be calculated first. The PWM frequency can be obtained by rearranging Equation 1. EQUATION 2: PWM FREQUENCY EQUATION Substituting the values of the PWM resolution ( 10 ) and oscillator frequency (4 MHz) to Equation 2 will yield a PWM frequency of Hz. PWM period is defined as shown in Equation 3. EQUATION 3: F OSC F PWM Resolution = log bits F PWM F = OSC 2 Resolution RELATIONSHIP OF PWM PERIOD AND PWM FREQUENCY PWM Period 1 = F PWM Using Equation 6 will yield a PR2 decimal value equal to 255 or a hexadecimal value FF. Any value greater than 255 will result in a 100% duty cycle. The PWM duty cycle is specified by writing to the CCPR2L register and to the DCxB1:DCxB0 (CCP2CON<5:4>) bits. Up to 10-bit resolution is available: the CCPR2L contains the eight MSbs and CCP2CON<5:4> contains the two LSbs. This 10-bit value is represented by CCPR2L and CCP2CON<5:4> in Equation 7. The code examples in Appendix A: Source Code in Assembly and Appendix B: Source Code in C use only 8 bits (CCPR2L) of resolution, so the CCP2CON<5:4> bits are programmed to a 0. The 8-bit A/D result is written into the CCPR2L register after each A/D conversion. This allows the PWM output to be controlled by the measured A/D value. The duty cycle can be calculated at any time using Equation 7. EQUATION 7: PWM DUTY CYCLE AT ANY TIME INSTANT PWM Duty Cycle = CCPR2L:CCP2CON<5:4> T OSC TMR2 prescale value Microchip Technology Inc. DS B-page 3

4 UNIVERSAL SYNCHRONOUS ASYNCHRONOUS RECEIVER TRANSMITTER (USART) The Universal Synchronous Asynchronous Receiver Transmitter (USART) module is one of the two serial I/O modules, the other being the SSP module. The USART is also known as a Serial Communications Interface or SCI. The USART can be configured as a full-duplex asynchronous system that can communicate with peripheral devices such as CRT terminals and personal computers, or it can be configured as a half-duplex synchronous system that can communicate with peripheral devices such as A/D or D/A integrated circuits, serial EEPROMs, etc. In the sample program, it is configured as a full-duplex asynchronous system to communicate with a personal computer. In this application note, the USART is only used for transmission. The registers needed to be set up are: Baud Rate Generator Register (SPBRG) Transmit Status and Control Register (TXSTA) Receive Status and Control Register (RCSTA) Transmit Data Register (TXREG) The init_usart code segment provides a sample configuration of the USART module (see Appendix A: Source Code in Assembly or Appendix B: Source Code in C ). The SPBRG is a dedicated 8-bit Baud Rate Generator. The SPBRG register controls the period of a free-running 8-bit timer. In Asynchronous mode, bit BRGH (TXSTA<2>) also controls the baud rate. In Synchronous mode, bit BRGH is ignored. To compute for the baud rate, Equation 8 is used. The TXSTA register is where the Asynchronous mode and the 8-bit transmission are selected. The Transmit Enable (TXEN) bit of the TXSTA register enables transmission and the Transmit Shift Register Status bit (TRMT) is a read-only bit which indicates the status of the Transmit Shift register (TSR). To start transmission, it is necessary to set the Serial Port Enable bit (SPEN) in the RCSTA register. Writing to the TXREG initiates the transmission. The code example copies the A/D result into the TXREG. The value is automatically moved into the TSR and shifted out on the RC6/TX pin. PERIPHERAL INTEGRATION After each peripheral is configured, the next step is to integrate them with each other. The LOOP code segment in the sample program shows how each peripheral is connected to each other (see Appendix A: Source Code in Assembly ). The program waits for TMR2IF to be set to signal the start of the Analog-to-Digital conversion. When A/D is done, the program waits again for the TRMT Flag bit to be set. After the conversion is completed, the A/D result is stored in the ADRES register and the ADRES value is copied to both the TXREG and CCPR2L registers to be outputted on the TX and CCP2 pins, respectively. EQUATION 8: Baud Rate BAUD RATE EQUATION F OSC = SPBRG Value + 1 Since the baud rate is set to 2400 baud, the SPBRG value will be obtained by rearranging Equation 8. EQUATION 9: SPBRG VALUE EQUATION F OSC SPBRG Value = Baud Rate 1 Substituting the value of FOSC = 4 MHz, an SPBRG decimal value of 25 will be obtained. Simply convert it into hex (19h) and load it into the SPBRG register. DS B-page Microchip Technology Inc.

5 FIRMWARE The firmware flowchart in Figure 2 combines both the configuration and integration processes discussed earlier. At first, all I/O ports are initialized. Serial ports are also enabled for USART transmission followed by the configuration of Timer2, A/D, CCP and USART peripherals. For the A/D, only one analog input channel is selected during the configuration process. Timer2 is enabled and the program starts polling the TMR2IF Flag bit. TMR2IF sets whenever a match between the TMR2 and PR2 registers takes place. When a match occurs, TMR2IF is then cleared in software and A/D conversion begins. After the A/D conversion is completed, the program monitors the TRMT bit to be set, indicating the TSR register of the USART is empty and ready for transmission. The A/D value is then written to the TXREG and CCPR2L registers. The next analog channel is then selected and the process is repeated. The USART and CCP outputs are received and processed by external hardware devices. FIGURE 2: FIRMWARE FLOWCHART Start Initialize PORTA Input Pins Initialize PORTC Output Pins Enable Serial Ports Clear TMR2 to PR2 Match Flag Bit Start A D Conversion Configure T 2 A/D Done? No Configure A/D Configure CCP for PWM mode Configure USART Yes TRMT = 1? No Enable Yes Put A D Value in TXREG TMR2IF = 1? No Put A D Value in CCPR2L Yes Switch Analog Input Channel Microchip Technology Inc. DS B-page 5

6 HARDWARE FIGURE 3: PIC16F7X/PIC16C7X DEMO SCHEMATIC DIAGRAM RP2 5 kω V DD C7 0.1 μf C1 15 pf C2 15 pf RP1 5 kω R2 470 Ω V DD X1 4 MHz U1 PIC16F7 / PIC16C7 V DD V DD MCLR CLKIN CLKOUT RE2 RE1 RE0 RA5 RA4 RA3 RA2 RA1 RB7 RB6 RB5 RB4 RB3 RB2 RB1 RB0 RD7 RD6 RD5 RD4 RD3 RD2 RD1 RD0 RC7 RC RA0 RC5 23 RC4 18 RC3 17 RC2 12 V SS 16 RC1 V SS 1 C3 0.1 μf 1 R1 330 Ω C4 0.1 μf C1- C2+ C2-1 T1IN T2IN R1OUT R2OUT C1+ U2 MA3232C GND V DD VCC C5 0.1 μf V+ V T1OUT 7 T2OUT 13 RB1IN 8 RB2IN R3 10 Ω C6 0.1 μf C8 0.1 μf P1 DE9S - FRS The schematic diagram of the hardware used in this application note is shown in Figure 3. It is basically a part of the PICDEM 2 Plus schematic with a few additional components. RP1 and RP2 trimpots are used to demonstrate a method of switching between analog input channels. They also determine the input voltage levels fed to the A/D. LED L1 is connected to the PWM output pin, RC1/CCP2, which is in series with the current limiting resistor, R1. U2 is an RS-232 line driver that provides electrical interface between the USART and the serial port connector, P1. DS B-page Microchip Technology Inc.

7 PROCESS FLOW FIGURE 4: SIMPLIFIED APPLICATION BLOCK DIAGRAM LED Brightness Analog Input Voltage A D USART Serial Terminal Display The application process flow is shown in Figure 4. When the analog input voltage is fed to the A/D, it converts the input voltage into a corresponding digital value. The input comes from AN0 or AN1 depending on the configured analog input channel. The digital results will be sent to both the USART and the CCP. The USART sends this value to a Serial Terminal Program, which displays an output value on a certain format depending on the terminal configuration. Likewise, the PWM of the CCP varies the duty cycle of the output pulse to control the brightness of an LED. SERIAL TRANSMISSION AND DISPLAY FIGURE 5: SERIAL TRANSMISSION BLOCK DIAGRAM USART PIC16F7X/PIC16C7X Serial Port Connector MCP2200 USB-to-UART Serial Converter USB Serial Terminal Program PICDEM 2 PLUS DEMO BOARD The USART output is sent to the Serial Terminal Program by connecting the USB-to-UART Serial Converter to the serial port connector included in the PICDEM 2 Plus Demo Board and to the USB port of a personal computer (see Figure 5). Microchip s MCP2200 is used as the USB-to-UART Serial Converter for this application. Since two analog channels are used in the A/D, two values will also be displayed on the PC monitor. A Serial Terminal Program is used to capture, control and debug binary streams of data. It must be setup to 2400 baud, eight data bits, one Stop bit and no parity to match the USART software configuration. The displayed value can also be set to either ASCII, ANSI, hexadecimal, binary or other types of numerical representation, depending on the Serial Terminal Program features Microchip Technology Inc. DS B-page 7

8 PWM DUTY CYCLE AND LED BRIGHTNESS Figure 6 shows sample PWM output waveforms with different input voltages. If only the input voltage across AN0 (V AIN0 ) is adjusted and AN1 voltage (V AIN1 ) is set to zero, waveforms (A) and (B) will result. Note that as the input voltage is increased, the Average Duty Cycle (DC AVE ) also increases. In addition, the Average DC Voltage (V DC ) across the PWM output pin also improves, making the LED output glow brighter. However, when the voltage across the AN1 pin is also adjusted, a much higher output can be attained. In (C) and (D), V AIN0 is set to its previous value and V AIN1 is set to 2V. This leads to much higher DC AVE and V DC values and, in turn, to a much brighter LED output. FIGURE 6: PWM OUTPUT WAVEFORMS (A) V AIN0 = 1V, V AIN1 = 0V, DC AVE = 11.82%, V DC = mv (B) V AIN0 = 3.5 V, V AIN1 = 0V, DC AVE = 40.45%, V DC = 1.535V CHS2:CHS (C) V AIN0 = 1V, V AIN1 = 2V, DC AVE = %, V DC = 1.358V (D) V AIN0 = 3.5V, V AIN1 = 2V, DC AVE = %, V DC = 2.491V The brightness of the LED connected to the CCP2 pin is determined by combining the settings of the two trimpots. A greater voltage across the two analog input pins, AN0 and AN1, will result in a higher duty cycle ratio and a brighter LED display output. Also, the maximum brightness will be achieved by setting the two trimpots to their maximum positions. The LED will be turned off when the two trimpots are in their minimum positions. DS B-page Microchip Technology Inc.

9 OUTPUT SIGNALS AND DISPLAY Figure 7 shows the summary of sample input and output signals. The analog input signals are purely DC voltages which are set to 2V and 4V for AN0 and AN1, respectively. When Channel 0 (CHS2:CHS0 = 000) is selected, the pulse width is narrow (i.e., a low duty cycle ratio). Moreover, the USART output and the serial decoding at the same instant are shown having a hex value of 4D. On the other hand, when Channel 1 is used (CHS2:CHS0 = 001), the pulse width is wider, which indicates a higher duty cycle ratio. The USART hex output is equal to E7, which is a much greater value than 4D. FIGURE 7: SUMMARY OF INPUT AND OUTPUT SIGNAL WAVEFORMS CHS2:CHS0 Analog Input PWM Output USART Output Serial Decoding A screen capture of a Serial Terminal Program output is shown in Figure 8. RealTerm, a freeware serial terminal software, is used for this example. The output is displayed as Hex[space] in Figure 8 to match the serial decoding values in Figure 7. The output s numerical representation and other display options can be selected under the Display menu in the RealTerm window Microchip Technology Inc. DS B-page 9

10 FIGURE 8: SERIAL TERMINAL PROGRAM DISPLAY The program is capable of producing an average DC voltage of almost 4.91V across the CCP2 pin output and a minimum voltage of a few microvolts. In addition, the USART output terminal display range is from 00h to FFh. The minimum and maximum output values depend mainly on the position of the two trimpots. Setting both trimpots to their minimum positions will produce minimum output values, and maximum output values for their maximum positions. To conclude, a greater voltage across the analog input terminal will result in a higher duty cycle ratio, a brighter LED output and a greater terminal display value. On the contrary, reducing the input voltage will also dim the LED and decrease the Serial Terminal display value. CONCLUSION In order to achieve the desired output values and display, it is often necessary to configure each peripheral one step at a time before putting them together. This application note describes a method on how the A/D, Timer2, CCP and USART are configured, implemented and integrated to achieve the desired A/D output values and display. Data are also provided to demonstrate how the peripherals behave at specific time instants. DS B-page Microchip Technology Inc.

11 APPENDIX A: SOURCE CODE IN ASSEMBLY Software License Agreement The software supplied herewith by Microchip Technology Incorporated (the Company ) is intended and supplied to you, the Company s customer, for use solely and exclusively with products manufactured by the Company. The software is owned by the Company and/or its supplier, and is protected under applicable copyright laws. All rights are reserved. Any use in violation of the foregoing restrictions may subject the user to criminal sanctions under applicable laws, as well as to civil liability for the breach of the terms and conditions of this license. THIS SOFTWARE IS PROVIDED IN AN AS IS CONDITION. NO WARRANTIES, WHETHER EXPRESS, IMPLIED OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE APPLY TO THIS SOFTWARE. THE COMPANY SHALL NOT, IN ANY CIRCUMSTANCES, BE LIABLE FOR SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES, FOR ANY REASON WHATSOEVER Microchip Technology Inc. DS B-page 11

12 EXAMPLE A-1: SAMPLE PROGRAM IN ASSEMBLY ;******************************************************************************* ; Revision Date: ; ; ; File Name: ; FACT003B.asm ; ; Summary: ; This is the main file used for the Application Note AN840 ; ; Hardware implementation requires: ; PICDEM2 PLUS DEMO BOARD ; ; Generation Information: ; Device : PIC16F74 ; Compiler : MPASM v5.54 ; MPLAB : MPLAB X 2.00 ;******************************************************************************* ;******************************************************************************* ;Copyright (c) 2013 released Microchip Technology Inc. All rights reserved. ; ;Microchip licenses to you the right to use, modify, copy and distribute ;Software only when embedded on a Microchip microcontroller or digital signal ;controller that is integrated into your product or third party product ;(pursuant to the sublicense terms in the accompanying license agreement). ; ;You should refer to the license agreement accompanying this Software for ;additional information regarding your rights and obligations. ; ;SOFTWARE AND DOCUMENTATION ARE PROVIDED AS IS WITHOUT WARRANTY OF ANY KIND, ;EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF ;MERCHANTABILITY, TITLE, NON-INFRINGEMENT AND FITNESS FOR A PARTICULAR PURPOSE. ;IN NO EVENT SHALL MICROCHIP OR ITS LICENSORS BE LIABLE OR OBLIGATED UNDER ;CONTRACT, NEGLIGENCE, STRICT LIABILITY, CONTRIBUTION, BREACH OF WARRANTY, OR ;OTHER LEGAL EQUITABLE THEORY ANY DIRECT OR INDIRECT DAMAGES OR EXPENSES ;INCLUDING BUT NOT LIMITED TO ANY INCIDENTAL, SPECIAL, INDIRECT, PUNITIVE OR ;CONSEQUENTIAL DAMAGES, LOST PROFITS OR LOST DATA, COST OF PROCUREMENT OF ;SUBSTITUTE GOODS, TECHNOLOGY, SERVICES, OR ANY CLAIMS BY THIRD PARTIES ;(INCLUDING BUT NOT LIMITED TO ANY DEFENSE THEREOF), OR OTHER SIMILAR COSTS. ;******************************************************************************* #include p16f74.inc CONFIG _FOSC_RC & _WDTE_OFF & _PWRTE_OFF & _CP_OFF & _BOREN_ON org 0x00 init_ports banksel TRISA ; goto bank 1 movlw 0x03 movwf TRISA ; set <Ra0:Ra1> as inputs movlw 0x00 movwf TRISC ; make all PORTC pins as output banksel RCSTA ; switch to bank 0 bsf RCSTA, SPEN ; enable serial ports DS B-page Microchip Technology Inc.

13 EXAMPLE A-1: SAMPLE PROGRAM IN ASSEMBLY (CONTINUED) init_adc banksel ADCON1 ; switch to bank 1 movlw 0x04 movwf ADCON1 ; set RA0, RA1, RA3 as analog ports, and Vref = Vdd banksel ADCON0 ; switch to bank 0 movlw 0xC1 movwf ADCON0 ; conversion clock = Frc ; set RA0/AN0 as analog channel ; turn on A/D Module init_pwm banksel PR2 ; switch to bank 1 movlw 0xFF movwf PR2 ; set value for TIMER2 Period Register banksel CCPR2L ; switch to bank 0 movlw 0x0F movwf CCPR2L ; set initial value for Capture/Compare/PWM Register2 movlw 0x0F movwf CCP2CON ; select PWM mode init_timer2 movlw 0x00 movwf T2CON ; prescale = 1:1, disable TIMER2 init_usart banksel SPBRG ; switch to bank 1 movlw 0x19 movwf SPBRG ; baud rate = 2400 for Fosc = 4 MHz movlw 0x20 movwf TXSTA ; enable asynchronous transmission banksel T2CON ; switch to bank 0 bsf T2CON, TMR2ON ; enable TIMER2 LOOP btfss PIR1, TMR2IF ; wait for TMR2 and PR2 to match goto $-1 bcf PIR1, TMR2IF ; clear TMR2 and PR2 match flag bit bsf ADCON0, GO ; start an A-to-D Conversion btfsc ADCON0, GO ; wait for conversion to complete goto $-1 banksel TXSTA ; switch to bank 1 btfss TXSTA, TRMT ; wait for TRMT flag bit to be set goto $-1 banksel ADRES ; switch to bank 0 movf ADRES, W ; move ADRES register value to W register movwf TXREG ; copy value on W register to TXREG movwf CCPR2L ; copy value on W register to Duty Cycle register movf ADCON0, W ; move ADCON0 register value to W register xorlw 0x08 movwf ADCON0 ; change analog input channel goto LOOP END Microchip Technology Inc. DS B-page 13

14 APPENDIX B: SOURCE CODE IN C EXAMPLE B-1: SAMPLE PROGRAM IN C /******************************************************************************* File Name: FACT003B.c Summary: This is the main file used for the Application Note AN840 Hardware implementation requires: PICDEM2 PLUS DEMO BOARD Generation Information : Device : PIC16F74 Compiler : XC8 v1.30 MPLAB : MPLAB X 2.00 *******************************************************************************/ /******************************************************************************* Copyright (c) 2013 released Microchip Technology Inc. All rights reserved. Microchip licenses to you the right to use, modify, copy and distribute Software only when embedded on a Microchip microcontroller or digital signal controller that is integrated into your product or third party product (pursuant to the sublicense terms in the accompanying license agreement). You should refer to the license agreement accompanying this Software for additional information regarding your rights and obligations. SOFTWARE AND DOCUMENTATION ARE PROVIDED AS IS WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY, TITLE, NON-INFRINGEMENT AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROCHIP OR ITS LICENSORS BE LIABLE OR OBLIGATED UNDER CONTRACT, NEGLIGENCE, STRICT LIABILITY, CONTRIBUTION, BREACH OF WARRANTY, OR OTHER LEGAL EQUITABLE THEORY ANY DIRECT OR INDIRECT DAMAGES OR EXPENSES INCLUDING BUT NOT LIMITED TO ANY INCIDENTAL, SPECIAL, INDIRECT, PUNITIVE OR CONSEQUENTIAL DAMAGES, LOST PROFITS OR LOST DATA, COST OF PROCUREMENT OF SUBSTITUTE GOODS, TECHNOLOGY, SERVICES, OR ANY CLAIMS BY THIRD PARTIES (INCLUDING BUT NOT LIMITED TO ANY DEFENSE THEREOF), OR OTHER SIMILAR COSTS. *******************************************************************************/ #include<xc.h> #pragma config FOSC = RC // Oscillator Selection bits (RC oscillator) #pragma config WDTE = OFF // Watchdog Timer Enable bit (WDT disabled) #pragma config PWRTE = OFF // Power-up Timer Enable bit (PWRT disabled) #pragma config CP = OFF // FLASH Program Memory Code Protection bit (Code protection off) #pragma config BOREN = ON // Brown-out Reset Enable bit (BOR enabled) void init_adc (void); void init_pwm (void); void init_timer2 (void); void init_usart (void); DS B-page Microchip Technology Inc.

15 EXAMPLE B-1: SAMPLE PROGRAM IN C (CONTINUED) void main (void) { TRISA = 0x03; // set RA0 and RA1 as inputs TRISC = 0xBD; // make PORTC pins as output SPEN = 1; // enable asynchronous serial ports init_adc (); init_pwm(); init_timer2(); init_usart (); TMR2ON = 1; while(1) { while(!tmr2if); // wait for TMR2 and PR2 match flag bit to be set TMR2IF = 0; // clear TMR2 and PR2 match flag bit GO_DONE = 1; // start an A-to-D Conversion while(go_done) // wait for conversion to complete { while(!trmt); // wait for TRMT flag bit to be set TXREG = ADRES; // put A/D result into TXREG register CCPR2L = ADRES; // put A/D result into Duty Cycle register } } } ADCON0 ^= 0x08; // change analog input channel void init_adc (void) { ADCON1 = 0x04; // set RA0, RA1, RA3 as analog ports, and Vref = Vdd ADCON0 = 0xC1; // conversion clock = Frc // set RA0/AN0 as analog channel // turn on A/D Module } void init_pwm (void) { PR2 = 0xFF; // PWM period = 256 us CCPR2L = 0x0F; // PWM duty cycle MSB CCP2CON = 0x0F; // PWM duty cycle LSB (CCP2CON<5:4> bits) } void init_timer2 (void) { T2CON = 0x00; // prescale = 1:1, disable TIMER2 } void init_usart (void) { SPBRG = 0x19; // baud rate = 2400 for Fosc = 4 MHz SYNC = 0; // select asychronous mode TXEN = 1; // enable asynchronous transmission } Microchip Technology Inc. DS B-page 15

16 Note the following details of the code protection feature on Microchip devices: Microchip products meet the specification contained in their particular Microchip Data Sheet. Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the intended manner and under normal conditions. There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip s Data Sheets. Most likely, the person doing so is engaged in theft of intellectual property. Microchip is willing to work with the customer who is concerned about the integrity of their code. Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not mean that we are guaranteeing the product as unbreakable. Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our products. Attempts to break Microchip s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act. Information contained in this publication regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer s risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights. QUALITY MANAGEMENT SYSTEM CERTIFIED BY DNV == ISO/TS == Trademarks The Microchip name and logo, the Microchip logo, dspic, FlashFlex, KEELOQ, KEELOQ logo, MPLAB, PIC, PICmicro, PICSTART, PIC 32 logo, rfpic, SST, SST Logo, SuperFlash and UNI/O are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. FilterLab, Hampshire, HI-TECH C, Linear Active Thermistor, MTP, SEEVAL and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A. Silicon Storage Technology is a registered trademark of Microchip Technology Inc. in other countries. Analog-for-the-Digital Age, Application Maestro, BodyCom, chipkit, chipkit logo, CodeGuard, dspicdem, dspicdem.net, dspicworks, dsspeak, ECAN, ECONOMONITOR, FanSense, HI-TIDE, In-Circuit Serial Programming, ICSP, Mindi, MiWi, MPASM, MPF, MPLAB Certified logo, MPLIB, MPLINK, mtouch, Omniscient Code Generation, PICC, PICC-18, PICDEM, PICDEM.net, PICkit, PICtail, REAL ICE, rflab, Select Mode, SQI, Serial Quad I/O, Total Endurance, TSHARC, UniWinDriver, WiperLock, ZENA and Z-Scale are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. SQTP is a service mark of Microchip Technology Incorporated in the U.S.A. GestIC and ULPP are registered trademarks of Microchip Technology Germany II GmbH & Co. KG, a subsidiary of Microchip Technology Inc., in other countries. All other trademarks mentioned herein are property of their respective companies , Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved. Printed on recycled paper. ISBN: Microchip received ISO/TS-16949:2009 certification for its worldwide headquarters, design and wafer fabrication facilities in Chandler and Tempe, Arizona; Gresham, Oregon and design centers in California and India. The Company s quality system processes and procedures are for its PIC MCUs and dspic DSCs, KEELOQ code hopping devices, Serial EEPROMs, microperipherals, nonvolatile memory and analog products. In addition, Microchip s quality system for the design and manufacture of development systems is ISO 9001:2000 certified. DS B-page Microchip Technology Inc.

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