EEE394 Microprocessor and Microcontroller Laboratory Lab #6

Transcription

1 Exp. No #6 Date: INTERRUPTS AND ADC IN PIC MICROCONTROLLER OBJECTIVE The purpose of the experiment is to configure external interrupt and the ADC in PIC microcontrollers. (i) To flip the LED connected to port using interrupt (ii) To convert analog signal to digital signal using ADC module in PIC. (iii) To display the analog voltage in LCD. PRE-LAB Complete the following study before starting the lab PIC16F877A Interrupts and ADC module PIC16Fxx reference manual THEORY INTERRUPTS An interrupt suspends the execution of the main program and a jump is executed to an interrupt service subroutine that takes some action in response to the interrupting condition and then returns control of the MCU back to the main program. The interrupt capable resources within the Microcontroller (MCU) can be divided into the two broad categories, those generated by external devices that are monitored by the MCU and internal resources. The external devices might include switches or sensors that are connected to I/O port pins, ADCs, or the comparator. The internal resources that can generate interrupts include TMRO and TMRI timer resources and write operations to internal Electrically Erasable Programmable Read-Only Memory (EEPROM.) PIC16F877 has many sources of interrupt. These sources generally include one interrupt source for each peripheral module, The current interrupts include INT Pin Interrupt (external interrupt), TMR0 Overflow Interrupt, PORTB Change Interrupt (pins RB7:RB4), Comparator Change Interrupt, Parallel Slave Port Interrupt, USART Interrupts, Receive Interrupt, Transmit Interrupt, A/D Conversion Complete Interrupt, LCD Interrupt, Timer1 Overflow Interrupt, Timer2 Overflow Interrupt, CCP Interrupt. One register used in the control and status of the interrupt is INTCON. Additionally, if the device has peripheral interrupts, then it will have registers to enable the peripheral interrupts and registers to hold the interrupt flag bits. These registers are named as PIR and PIE. Page 58

2 A/D CONVERTER The analog-to-digital (A/D) converter module has up to eight analog inputs for a device. The converter then generates a digital result of this analog level via successive approximation. This A/D conversion, of the analog input signal, results in a corresponding 10-bit digital number. The analog reference voltages (positive and negative supply) are software selectable to either the device s supply voltages (AV DD, AVss) or the voltage level on the AN3/V REF + and AN2/V REF pins. The A/D module has four registers. These registers are: A/D Result High Register (ADRESH), A/D Result Low Register (ADRESL), A/D Control Register0 (ADCON0), A/D Control Register1 (ADCON1). The ADCON0 register controls the operation of the A/D module. The ADCON1 register configures the functions of the port pins. Page 59

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4 A/D Result Registers The ADRESH : ADRESL register pair is the location where the 10-bit A/D result is loaded at the completion of the A/D conversion. This register pair is 16-bits wide. The A/D module gives the flexibility to left or right justify the 10-bit result in the 16-bit result register. The A/D Format Select bit (ADFM) controls this justification. The following steps should be followed for doing an A/D conversion: 1. Configure the A/D module: Configure analog pins / voltage reference/ and digital I/O (ADCON1) Select A/D input channel (ADCON0) Select A/D conversion clock (ADCON0) Turn on A/D module (ADCON0) 2. Configure A/D interrupt (if desired): Clear the ADIF bit Set the ADIE bit Set the GIE bit 3. Wait the required acquisition time. 4. Start conversion: Set the GO/DONE bit (ADCON0) 5. Wait for A/D conversion to complete, by either: Polling for the GO/DONE bit to be cleared or ADIF bit to be set OR Waiting for the A/D interrupt 6. Read A/D Result register pair (ADRESH:ADRESL), clear the ADIF bit, if required. 7. For next conversion, go to step 1 or step 2 as required. Acquisition time is the time that the A/D module s holding capacitor is connected to the external voltage level. Then there is the conversion time of 12 T AD, which is started when the GO bit is set. The sum of these two times is the sampling time. There is a minimum acquisition time to ensure that the holding capacitor is charged to a level that will give the desired accuracy for the A/D conversion. Page 61

5 TASK #1 Consider two LED s connected to any of the ports. Write a program to flash LED1 for every 1sec and flip the digital output of LED2 using interrupt with the switch connected to the interrupt pin. Consider an interrupt to flip LED2 every time a rising edge is detected on the interrupt pin. Meanwhile, LED1 will continue to flash. Circuit Design Current Limiting Resistor Let I = LED forward current in Amps (from LED datasheet), V f = LED forward voltage drop in Volts (from LED datasheet) and V = microcontroller output pin voltage. R = V V f / I = Design Implementation GPIO and interrupt selection Algorithm / Program flow Page 62

6 Source code #1 Testing and Verification (i) Check the output using Logic Analyzer in MPLAB IDE / implement the circuit in PROTEUS. (ii) Implement the circuit in development board and verify the task. Discussion & Inference Page 63

7 TASK #2 Write a simple program in C language to convert analog voltage connected to ADC pin to digital signal using ADC module in PIC. Use 8 LEDs to flash the converted values. Circuit Design Algorithm / Program flow Page 64

8 Source code #2 Testing and Verification Implement the circuit in PROTEUS and verify the task. Discussion & Inference Page 65

9 ADDITIONAL TASK (Optional) Write a simple program in C language to measure temperature using LM35 and display in LCD. Circuit Design Source code Page 66

10 Testing and Verification Discussion & Inference Page 67

11 UNDERSTANDING & LEARNING Prepared by: Name: Reg. No.: Experiment Date: ASSESSMENT Report Submission Date: Submission Delay:... Student Task Max.Marks Graded Marks Pre-lab Preparation 10 Program flow / logic 10 Design / Implementation 10 Signature Post-lab / Viva-voce 10 Total 40 Page 68