EE 308 Lab 6 Spring 2003EE 308 – LAB 6Using the HCS12 Timer Overflow Interrupt and Real Time InterruptIntroductionEnabling an interrupt on the HCS12 allows your program to respond to an external event withoutcontinually checking to see if that event has occurred. Once the event occurs, the HCS12 interruptsubsystem will transfer control of your program to an interrupt service routine (ISR) to handlethe event, and then return control to your original code sequence. In this week’s lab you willwrite assembly and C language programs which enable and use interrupts. Note that it is difficult(although not impossible) to simulate interrupts on the ZAP simulator, so we will not do that forthis lab.The interrupts on the HCS12 which are easiest to use are the Timer Overflow Interrupt and theReal Time Interrupt. These interrupts allow you to interrupt the HCS12 after a specified amountof time has passed.Pre-LabFor the pre-lab, write the programs for Sections 6 and 7. Also, calculate the time asked for inPart 5.The Lab1. Connect your HCS12 to your computer. At the D-Bug12 prompt, display the contents of theTCNT register. Do this several times. How do the values compare?2. Use D-Bug12 to modify the TSCR1 register to enable the counter. Repeat Part 1.3. Use D-Bug12 to modify the TSCR1 register to disable the counter. Repeat Part 1.4. Start with the follwing do-nothing program:prog: equ $1000stack: equ $3C00CODE: section .text ;The stuff which follows is program codeorg proglds #stackloop: waijmp loopAdd code to make PORTA an output port. Then add a Timer Overflow Interrupt to incrementthe four lower bits of PORTA. Set the timer overflow rate to b e 175 ms. You should incrementthe four lower bits of PORTA in the interrupt service routine, and leave the four upper bits1EE 308 Lab 6 Spring 2003of PORTA unchanged. Connect the eight pins of PORTA to the LEDs on the breadboard andverify that the lower four bits of PORTA function as an up-counter.Note: To use interrupts in an assembly language program you will need to add a vector.s filewhich contains the addresses of the interrupt vectors. Here is a vector.s file for a programwhich uses the TOI interrupt:xdef toi_isr ; toi_isr is defined in another fileVECTOR: section .textorg $3e5e ; Address of timer overlow interrupt in D-Bug 12dc.w toi_isr ; Put address of toi_isr hereBecause the vector.s file refers to toi_isr which is in another file, you need the follow ing inthe file where toi_isr is defined:xref toi_isr ; Export name so vector.s can use itYou then need a linker file to link the main program and the vector.s program:+seg .text -b 0x1000 -n .text+seg .text -b 0x2000 -n .datatoi.o+seg .text -b 0x3E00 -n .textvector.oYou need to assemble both the main program and the vector.s file. Here is a batch file w hichdoes this:c:\cx32\ca6812 -a -l -xx -pl %1.s vector.sc:\cx32\clnk -o %1.h12 -m %1.map %1.lkfc:\cx32\chex -o %1.s19 %1.h125. Calculate how long it should take the for lower bits of PORTA to count from 0x0 to 0xF androll over to 0x0. Use a watch to measure the time. How do the two times agree?6. Add a Real Time Interrupt to your assembly language program. Set up the RTI to generatean interrupt every 65.536 ms. In the RTI interrupt service routine, implement a rotating biton the four upper bits of PORTA, while leaving the four lower bits of PORTA unchanged. Verifythat the bit takes the correc t amount of time to rotate through the four upper bits.A rotating bit will look like this:· · · •· · • ·· • · ·• · · ·· · · •· · • ·· • · ·• · · ·2EE 308 Lab 6 Spring 20037. Implement the same program in C.8. Change your C program so that you do not reset the Timer Overflow Flag in the TimerOverflow ISR. Does your up-counter work? Does your rotating bit work? Why?9. Restore your original C program from Part 7. Now change your C program so that you donot reset the Real Time Inte rrupt Flag in the Real Time Interrupt ISR. Does your up-counterwork? Does your rotating bit work? Why?10. Restore your original C program from Part 7. Change your vecdp256.c file to put a 0 in forthe address of the Timer Overlow Interrupt. Run you program. What happens now? Why?To add interrupt vectors in C you will need a file listing the addresses of the interrupt serviceroutines. Note that different versions of the HCS12 have different interrupt vectors, and hence usedifferent vector files. Here is a file called vecdp256.c for 68HC912B32 chip:/* INTERRUPT VECTORS TABLE FOR MC9S12DP256B*/void toi_isr(); /* define all used ISR names here *//* Vectors start at 0xFF80 on standard MC9S12DP256B;* remapped to RAM by D-Bug 12, starting at 0x3E00 */void (* const _vectab[])() = {/* Flash DB12 */0, /* Reserved (FF80) (3E00) */0, /* Reserved (FF82) (3E02) */0, /* Reserved (FF84) (3E04) */0, /* Reserved (FF86) (3E06) */0, /* Reserved (FF88) (3E08) */0, /* Reserved (FF8A) (3E0A) */0, /* PWM Emergency Shutdown (FF8C) (3E0C) */0, /* Port P (FF8E) (3E0E) */0, /* MSCAN4 XMT (FF90) (3E10) */0, /* MSCAN4 RCV (FF92) (3E12) */0, /* MSCAN4 ERR (FF94) (3E14) */0, /* MSCAN4 WAKE (FF96) (3E16) */0, /* MSCAN3 XMT (FF98) (3E18) */0, /* MSCAN3 RCV (FF9A) (3E1A) */0, /* MSCAN3 ERR (FF9C) (3E1C) */0, /* MSCAN3 WAKE (FF9E) (3E1E) */0, /* MSCAN2 XMT (FFA0) (3E20) */0, /* MSCAN2 RCV (FFA2) (3E22) */0, /* MSCAN2 ERR (FFA4) (3E24) */0, /* MSCAN2 WAKE (FFA6) (3E26) */0, /* MSCAN1 XMT (FFA8) (3E28) */0, /* MSCAN1 RCV (FFAA) (3E2A) */0, /* MSCAN1 ERR (FFAC) (3E2C) */0, /* MSCAN1 WAKE (FFAE) (3E2E) */3EE 308 Lab 6 Spring 20030, /* MSCAN0 XMT (FFB0) (3E30) */0, /* MSCAN0 RCV (FFB2) (3E32) */0, /* MSCAN0 ERR (FFB4) (3E34) */0, /* MSCAN0 WAKE (FFB6) (3E36) */0, /* Flash (FFB8) (3E38) */0, /* EEPROM (FFBA) (3E3A) */0, /* SPI2 (FFBC) (3E3C) */0, /* SPI1 (FFBE) (3E3E) */0, /* IIC (FFC0) (3E40) */0, /* DLC (FFC2) (3E42) */0, /* SCME (FFC4) (3E44) */0, /* CRG Lock (FFC6) (3E46) */0, /* PACTLB Overflow (FFC8) (3E48) */0, /* Modulus Down Counter Underflow (FFCA) (3E4A) */0, /* PORTH (FFCC) (3E4C) */0, /* PORTJ (FFCE) (3E4E) */0, /* ATD1 (FFD0) (3E50) */0, /* ATD0 (FFD2) (3E52) */0, /* SCI1 (FFD4) (3E54) */0, /* SCI0 (FFD6) (3E56) */0, /* SPI0 (FFD8) (3E58) */0, /* PACTLA Input Edge (FFDA) (3E5A) */0, /* PACTLA Overflow (FFDC) (3E5C) */toi_isr, /* Timer Overflow (FFDE) (3E5E) */0, /* Timer channel 7 (FFE0) (3E60) */0, /* Timer channel 6 (FFE2) (3E62) */0, /* Timer channel 5 (FFE4) (3E64) */0, /* Timer channel 4 (FFE6) (3E66) */0, /* Timer channel 3 (FFE8) (3E68) */0, /* Timer channel 2
View Full Document
Unlocking...