PIC Basic Interrupt Structure and Programming

Transcription

PIC Basic Interrupt Structure and
Programming
Interrupt I/O
Interrupts capabilities are desirable when a
system must be responsive to external,
asynchronous events
CpE 112 : Klinkhachorn
Polling I/O
✔ Start device and poll for completion
Program Execution
.
.
Start Device
Input status
Poll and Wait
Until Device Ready
…
Interrupt I/O
✔ Start device and continue program execution
Program Execution
.
.
Start Device
.
.
.
.
…
ISR
Procedure
For device
Service
Routine
.
RETURN
PIC Interrupt Sequence
✔ When interrupt occurs
– CPU automatically pushes the return address in
the Program Counter on to the stack
– CPU clears the Global Interrupt Enable (GIE)
bit (disable further interrupts)
✔ This is it …..no other registers or W are
automatically set aside!!!!!
16F87X Interrupt
✔ The PIC16F87X family has up to 14
sources of interrupt.
Timer0 interrupt
External interrupt on RB0/INT (programmable edge trigger)
PortB change interrupt (RB7:RB4)
Parallel Slave Port interrupt
Analog to digital interrupt
UART Receive interrupt
UART Transmit Empty interrupt
Synchronous Serial Port interrupt
Compare/Capture/PWM-1 interrupt
Timer2 interrupt
Timer1 interrupt
EEPROM interrupt
Bus Collision(I2C) interrupt
Compare/Capture/PWM-2 interrupt
16F87X Interrupt Logic
Power-down Mode: SLEEP
✔ Power-down mode is entered by executing a
SLEEP instruction.
– If enabled, the Watchdog Timer will be cleared but
keeps running
• the PD/ bit (STATUS<3>) is cleared
• the TO/ (STATUS<4>) bit is set
– the oscillator driver is turned off
– the I/O ports maintain the status they had before the
SLEEP instruction was executed (driving high, low, or
hi-impedance)
Wake-up from SLEEP
✔ One of the following events can wake
up the CPU
– External reset input on MCLR/ pin
– Watchdog Timer Wake-up (if WDT was
enabled)
– Interrupt from INT pin, RB port change, or
some peripheral interrupts (e.g. PSP read/write,
TMR1, CCP, SSP, USART RX, TX, A/D, and
EEPROM write operation
Wake-up through an Interrupt Event
✔ The corresponding interrupt enable bit must
be set
– If global interrupt is disabled
• The CPU continues execution at the instruction after
the SLEEP instruction
– If global interrupt is enabled
• The CPU executes the instruction after the SLEEP
instruction and then branches to the interrupt vector
(004h)
Wake-up from SLEEP through Interrupt
Interrupt Control Register
✔ The interrupt control register (INTCON)
records individual interrupt requests in
flag bits
– It also has individual and global interrupt
enable bits.
7
0
Global Interrupt Enable
✔ A global interrupt enable bit, GIE (INTCON<7>)
enables (if set) all unmasked interrupts, or disables (if
cleared) all interrupts
– When bit GIE is enabled, and an interrupt’s flag bit and mask
bit are set, the interrupt will vector immediately
– Individual interrupts can be disabled through their
corresponding enable bits in various registers
– Individual interrupt bits are set, regardless of the status of
the GIE bit
✔ The GIE bit is cleared on RESET.
✔ The “return from interrupt” instruction, RETFIE, exits
the interrupt routine, as well as sets the GIE bit,
which reenables interrupts.
Code Template
✔ Explanatory remarks
✔ Assembler directives
✔ Equates to give names to numbers
✔ Variable definitions
✔ Reset and interrupt vector
✔ A table
✔ Mainline code and its subroutines
✔ Initialization code
✔ Interrupt service routine
– Systematic handling of W and STATUS
– Polling routine
– Specific interrupt handling subroutine
Reset and interrupt vector (same Page)
org H‘000’
goto mainline
;Reset vector
;start main program
org H‘004’
;Interrupt vector
goto IntService ;jump to ISR
;if the ISR is located in the same Program
; Memory bank of the main program otherwise
; save W, Status, PCLATH
; then select the proper bank (PCLATH<4:3>)
;before jump to ISR!
Initialization code for Interrupts
Mainline ….
….
;initialize any required registers and variables
;Enable any required interrupt mask, e.g. INTE.
;
bsf INTCON, INTE ; Enable external interrupt
…..
;Then enable Global Interrupt
bsf INTCON, GIE
; Enable global interrupts
Interrupt service routine (same Page)
IntService
;save W and Status Registers
movwf
swapf
W_temp
STATUS,W
; store W in W_Temp
;move status to W
;without affecting z bit!
movwf Status_Temp
;save STATUS
;Polling interrupt flag and goto specific interrupt handler routines
;do what it need to be done
.
;on exit
;restore STATUS and W then return
swapf
Status_Temp,W
;restore STATUS (swap nibbles)
movwf STATUS
;without affecting z bit!
swapf
W_temp,F
;swap W_temp
swapf
W_temp, W
;swap again to restore W
;without affecting z bit
retfie
;Return to …. and reenable the interrupts
Reset and interrupt vector (different page)
org H‘000’
goto mainline
;Reset vector
;start main program
org H‘004’
;Interrupt vector
movwf
swapf
movwf
swapf
movwf
bsf
goto
;store W in W_Temp
;move status to W without affecting z bit!
;save STATUS
;move PCLATH to W without affecting z bit!
;save PCLATH
;Switch to page 1
W_temp
STATUS,W
Status_Temp
PCLATH, W
PCLATH_Temp
PCLATH,3
IntService
;jump to ISR
Interrupt service routine (different page)
IntService
;Polling interrupt flag and goto specific interrupt handler routines
;do what it need to be done
.
;on exit
; ON exit restore PCLATH, STATUS and W
swapf PCLATH_Te mp, W
;Restore PCLATH
m ovwf PCLATH
;Move W into PCLATH
swapf Status_Te mp,W
;Swap Status_Te mp register into
W
;(sets data me mory bank to original state)
m ovwf STATUS
swapf W_Tem p,F
swapf W_Tem p, W
Retif
;Move W into STATUS register
;Swap W_Tem p
;Swap W_Tem p into W
;Bye
Interrupt: Polling and Service Interrupt
IntService
;Polling routine
btfsc Register_Nam e,Flag_bit;Arrange from the
;highest priority
;interrupt source
goto Interrupt_A
;if set, do it!
btfsc ...
;check next highest
;priority…
goto ...
;if set, go for it
.
.
;repeat until get to the lowest interrupt source
Done
;restore the necessary registers
Interrupt: CCS PIC C-Complier
#Priority rtcc,rb,.. ;set interrupt priority
;The highest is first
#INT_GLOBAL Na me()
{
//your codes
}
;replace the co mplier
;interrupt dispatcher
;you must take care
;all of registers saving
;and etc.
#INT_xxx Na me()
{
; your codes
}
CCS support the following:
INT_EXT (External Interrupt)
INT_RTCC (Timer0 [RTCC] overflow)
INT_RB
(Change on B4-B7 PIN)
INT_AD
(A/D Converter)
INT_TIMER1 (Timer1 overflow)
INT_SSP (S mart Serial Port (SPI,I2C))
INT_PSP (Parallel Slave Port)
...
DISABLE_INTERRUPTS(XXX)
W here XXX is
Global
(GIE)
INT_RB
INT_AD
(A/D Converter)
…
Exa mple: disable_interrupts(global);
ENABLE_INTERR UPTS(XXX)
W here XXX is
Global
(GIE)
INT_RB
INT_AD
(A/D Converter)
…
Exa mple: enable_interrupts(global);
INT Interrupt (External)
✔ External interrupt on the RB0/INT pin is edge triggered
– rising, if bit INTEDG (OPTION_REG<6>) is set
– falling, if the INTEDG bit is clear
✔ When a valid edge appears on the RB0/INT pin, flag bit
INTF(INTCON<1>) is set
– can be disabled by clearing enable bit INTE (INTCON<4>)
✔ Flag bit INTF must be cleared in software in the interrupt service
routine before reenabling this interrupt
✔ The INT interrupt can wake-up the processor from SLEEP, if bit
INTE was set prior to going into SLEEP
– The status of global interrupt bit decides whether or not the
processor branches to the interrupt vector following wakeup.
External Interrupt: CCS PIC C-Complier
EXT_INT_EDGE(edge)
W here edge is
L_to_H
H_to_L
Exa mple: ext_int_edge(L_to_H);
EXT Interrupt : Example
✔ Rotary Encoder - rotary pulse generator (RPG)
– Applications
• Volume and Tone Control forAudio Visual Equipment
• Tuner for Communication Units
• Mode selection for Measurement
Rotary Encoder: Example
✔ Available in mechanical (few $) or optical ($10+)
Rotary Encoder: Example
✔ Phase Difference
One cycle
ON/OFF
determines CCW/CW
INT_EXT Interrupt : Example
Main Program
.
.
.
.
enable_interrupts(int_EXT);
enable_interrupts(global);
.
.
.
INT_EXT Interrupt : Example
#int_ext
EXT_INT_ISR()
{
// one interrupt per cycle
// determine direction by reading the another bit
// do what is necessary
// exit
}
Note: CCS will reset INTE flag and re-enable GIE.
These do not applied to #int_Global!
INT_RB Interrupt : Example
Port B <4:7>
External Inputs
PIC16F877
Main Program
.
.
.
.
enable_interrupts(int_RB);
enable_interrupts(global);
.
.
.
#int_rb
RB_ISR()
{ Byte changes;
changes = last_b ^ port_b;
last_b = port_b;
if (bit_test(changes,4) && !bit_test(last_b,4))
{ // bit 4 went low do something….}
.
.
delay_ms(10);
//debouncing! Not recommended!
}
Note: CCS will reset RBinterrupt flag and re-enable GIE.
These do not applied to #int_Global!
TIMERs/COUNTERs
✔ PIC16F877
–Timer0
–Timer1
–Timer2
Timer0 Module
• 8-bit timer/counter
• Readable and writable
• 8-bit software programmable prescaler
• Internal or external clock select
• Interrupt on overflow from FFh to 00h
• Edge select for external clock
Timer0/WDT Block diagram
•
Timer0 - Prescaler Assignment
•
Watch Dog Timer
✔ Run on internal RC
– If enable during SLEEP mode, WDT will
continue running and will be able to wake up
the processor on Time-out!
✔ With Prescaler (Post) set to 1:128, typical
maximum delay time can be approximately
18*128 ms or over 2 seconds!
Timer0 - TMR0 - Register
✔ All instructions writing to the TMR0 will clear
the prescaler count, but not change the
prescaler assignment!
– i.e. clrf TMR0, movwf TMR0, ….etc.
✔ The TMR0 interrupt is generated when the
TMR0 register overflows from FFh to 00h
✔ TMR0 interrupt cannot awaken the processor
from SLEEP (the timer is off during the
SLEEP)
Timer0 - Registers associated
Timer1 Module
• 16-bit timer/counter (TMR1H,TMR1L)
• Readable and writable (both)
• Internal or external clock select
• Interrupt on overflow from FFFFh to 0000h
• Reset from CCP module trigger
• Programmable Prescaler (1,2,4, and 8)
• Sync and Asyn Counter mode
Timer1Block diagram
•
Timer1 - T1CON - Control Register
•
Timer1 Oscillator
✔ Low power Oscillator rated upto 200kHz
– Primary intended for a 32kHz
✔
Will run during SLEEP
Timer1 - TMR1H:TMR1L
✔ The register pair (TMR1H:TMR1L)
increments from 0000h to FFFFH and rolls
over to 0000H
✔ Interrupt if enabled (TMR1IE) on overflow
(set TMR1IF)
Timer2 Module
• 8-bit timer (TMR2)
• 8-bit period register (PR2)
• Readable and writable (both)
• Interrupt on TMR2 match of PR2
• Programmable Prescaler (1,4, and 16)
• Programmable postscaler (1 to 16)
• Can be use as the PWM time-base for PWM mode of the
CCP module
• SSP module optional use of TMR2 output to generate clock
shift
Timer2 Block diagram
•
Timer2 - T2CON - Control Register
•
Timer2 - TMR2
✔ The prescaler and postscaler counters are
cleared when any of the following occurs:
– A write to the TMR2
– A write to the T2CON
– Any device reset
✔ TMR2 is not cleared when T2CON is written

PIC Basic Interrupt Structure and Programming

Transcription

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