ECE 371 – Unit 9

Interrupts (continued)

Example

• Set up Two Interrupt Request Inputs:

– Port H[0] Set Interrupt Flag on “0” to “1” transition (rising edge)

• Port H[1] Set Interrupt Flag on “1” to “0” transition (trailing edge)

Example (cont)

Response to Interrupts:

• Toggle H[4] on each H[0] Interrupt

• Toggle H[5] on each H[1] Interrupt

#include ece371.h/* Port H Port Definitions */#define PTH _P( 0x260)#define PTIH _P( 0x261)#define DDRH _P( 0x262)#define RDRH _P( 0x263) #define PERH _P( 0x264) #define PPSH _P( 0x265) #define PIEH _P( 0x266) #define PIFH _P( 0x267)

Example – Port H Interrupt

Interrupt Service Routine

Setting up (declaring) “myisr” as in Interrupt Service Routine:

void myisr() __attribute__ ((interrupt)); //should be at the //beginning of source file

/* 2 underscores before and after attribute */

/* Do not use #pragma, which is used in the text To establish in Interrupt Service Routine*/

#include <ece371.h>#include <ports_D256.h>void myisr() __attribute__ ((interrupt));

int main() {/* stack is initialized by c */

/* initialize interrupt vector for Port H */ SETVECT(0xFFCC,my_isr);

/* init Data Direction Bits for Port HBits 0 and 1 are InputBits 4 and 5 are OutputOther Bits assigned to other

applications /* DDRH = DDRH & 0xFC; // Bit 0 and 1 are Input DDRH = DDRH | 0x30; // Bit 4 and 5 are output

Example – Main Program

/* Set Bit 4 and 5 to full drive outputs */ RDRH = RDRH & 0xCF; //11001111

/* Enable Bit 0 and 1 Pull Device on Input */ PERH = PERH | 0x03; // Enable Bit 0 and 1 Pull Device PPSH = (PPSH & 0xFC) | 0x01; // Bit 0 Rise, Bit 1 Fall

/* Clear Pending Port H Bit 0 and 1 Interrupts */ PIFH = 0x03;

/* Enable Bit 0 and 1 to Interrupt */ PIEH = PIEH | 0x03; // Enable Interrupts

/* Enable Maskable Interrupt System */ ENABLE();

/* do main program processing */ while(TRUE); // loop}

void my_isr(void) { if ((PIFH&0x2)!=0) {//Bit 1 was source of interrupt PIFH = 0x02; // Clear Interrupt // Do interrupt specific action, complement Bit 5 PTH = PTH ^ 0x20; } if ((PIFH&0x01)!=0) {//Bit 0 was source of interrupt PIFH = 0x01; // Clear Interrupt // Do interrupt specific action, complement Bit 4 PTH = PTH ^ 0x10; } }

Example Interrupt Handler

• Use Each Bit of Port H as an Interrupt Request Input

• Count the Running Total of Interrupt Request that Occur on Each of the 8 Request Inputs

Another Example: 8-Switch CounterImplemented Using Interrupts

#include <ece371.h>#include <ports_D256.h>void myisr() __attribute__ ((interrupt));/* Port H definitions go here */int count[8]=0,0,0,0,0,0,0,0; // globalint main() {/* stack is initialized by c */

/* initialize interrupt vector for Port H */ SETVECT(0xFFCC,my_isr);

/* Init Data Direction Bits for Port HAll bits are input

/* DDRH = 0x00;

Another Example: (cont)

/* Enable Pull Devices on Port H all bits */ PERH = 0xFF; /* Interrupt on “1” to “0” Transitions all bits PPSH = 0x00;

/* Clear Pending Port H Interrupts all bits */ PIFH = 0xFF;

/* Enable all Port H bits to Interrupt */ PIEH = 0xFF; // Enable Interrupts

/* Enable Maskable Interrupt System */ ENABLE();

/* do main program processing */ while(TRUE); // loop}

void my_isr(void) { int i; for(i=0;i<8;i++) {if ((PIFH & (1<<i))!=0) {//Bit i was source of interrupt PIFH = (1<<i); // Clear Interrupt // Do interrupt specific action count[i]++; } } }

Method 1 for Implementing Interrupt Service Routine

void my_isr(void) { int i; unsigned char change; change = PIFH; // change bitsw PIFH = change; // Clear interrupt flag for(i=0, i<8, i++) if(((change>>i)&0x01)!=0) {count[i]++;} }

Method 2 for Implementing Interrupt Service Routine

Still Another Example: Interfacing a Keypad (Fig. 5.5) Using Interrupts

Use Port H

Keypad with Interrupts

• Port H[3:0]– Output– Full Drive– Set Bits to “0” (all at once)

• Port H[7:4]– Input– Interrupt on “1” to “0” (Key Pressed)

Cflag!=0 ?

c=cin;cflag=0;

Function “ci” to Read Keypad

ScanKeypad

cin=keypad charactercflag=1;

Interrupt

Main –ISR CommunicationShared Variables

==0

!=0

Intr. Service Routine

Passing Parameters Between Main Program and Interrupt Service Routine

unsigned char cin, cflag=0; /*global variables declared outside Interrupt Service Routine and all functions/*

//function to read keyboard:unsigned char ci(void){ while(cflag == 0); cflag=0; return cin;}

Main Program – Receiving Character from ISR

Int main(){ unsigned char c; PTH=0; // select all rows ENABLE(); // enable all interrupts ---- c=ci(); // input character from keypad //function ci defined on previous slide

----}

Tasks for Keypad ISR

• On a Port H Interrupt:– Clear Interrupt Flag Register with Write– Scan Keypad for Pressed Key– cin=key; cflag=1:– Set Port H outputs to “0

void kbisr() //define ISR{unsigned char mask[4]=0x0E,0x0D,0x0B,0x07;int i,j;

//1110, 1101, 1011, 0111 PIFH = PIFH; // clear interrupt request for(i=0;i<4;i++) {PTH = mask[i]; // assert row in keypad for(j=0;j<4;j++) {if((PTH>>4) == mask[j]) {if (((i<<2)+j)<10) {cin = ‘0’+(i<<2)+j;cflag=1;} else cin=‘A’+(i<<2)+j -10;cflag=1;} } } PTH = 0x00; // select all rows}

Keypad ISRvoid kbisr() __attribute__ ((interrupt)); //Establish kbisr as ISR