PIC Interrupts
Introduction:
PIC16F877 has 14 interrupt sources. The following registers are used for setting the interrupt and checking the status of the interrupt. These are
- INTCON Register (04 registers, duplicated in each bank addresses 0Bh, 8Bh, 10Bh, 18Bh)
- PIE1 Register (Address 8Ch )
- PIR1 Register (Address 0Ch)
- PIE2 Register (Address 8Dh)
- PIR2 Register( Address 0Dh)
Figure-1 illustrates how the request from the interrupt source is communicated to the CPU.
Table-1 shows the various sources of interrupts, and the registers used to enable the interrupts and the status flags
| Type
|
Interrupt Register SFR Address | REGISTER | INTERRUPT ENABLE BIT | INTERRUPT FLAG BIT | STATUS FLAG REGISTER | Status(Flag) Register SFR Address |
| Global | 0Bh / 8Bh/10Bh, 18Bh | INTCON | GIE | |||
| Peripheral | 0Bh / 8Bh/10Bh, 18Bh | INTCON | PEIE | |||
| Timer0 | 0Bh / 8Bh/10Bh, 18Bh | INTCON | T0IE | T0IF | INTCON | 0Bh / 8Bh |
| External | 0Bh / 8Bh/10Bh, 18Bh | INTCON | INTE | INTF | INTCON | 0Bh / 8Bh |
| PortB | 0Bh / 8Bh/10Bh, 18Bh | INTCON | RBIE | RBIF | INTCON | 0Bh /8Bh |
| Parallel Slave Port Read/Write
|
8Ch | PIE1 | PSPIE | PSPIF | PIR1 | 0Ch |
| ADC | 8Ch | PIE1 | ADIE | ADIF | PIR1 | 0Ch |
| USART Receive
|
8Ch | PIE1 | RCIE | RCIF | PIR1 | 0Ch |
| USART Tx
|
8Ch | PIE1 | TXIE | TXIF | PIR1 | 0Ch |
| Synchronous Serial Port
|
8Ch | PIE1 | SSPIE | SSPIF | PIR1 | 0Ch |
| CCP1 | 8Ch | PIE1 | CCP1IE | CCP1IF | PIR1 | 0Ch |
| TMR2 to PR2 Match
|
8Ch | PIE1 | TMR2IE | TMR2IF | PIR1 | 0Ch |
| TMR1 Overflow Interrupt | 8Ch | PIE1 | TMR1IE | TMR1IF | PIR1 | 0Ch |
| CCP1 | 8Dh | PIE2 | CCP2IE | CCP2IF | PIR2 | 0Dh |
| Bus Collision
|
8Dh | PIE2 | BCLIE | BCLIF | PIR2 | 0Dh |
| EEPROM Write Operation
|
8Dh | PIE2 | EEIE | EEIF | PIR2 | 0Dh |
Table below shows a summary of the registers being used for configuring the interrupts and to know their status. INTCON, PIE1, PIE2 are used to configure the interrupts whereas PIR1, PIR2 are the status or the flags for these interrupt, INTCON also shows the status for three interrupts RBIE, INTE, and TOIE interrupts
| Bank | Address | Name | D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 | Value on: POR, BOR |
| 0 / 1/2/3 | 0Bh / 8Bh/10Bh/18Bh | INTCON | GIE | PEIE | T0IE | INTE | RBIE | T0IF | INTF | RBIF | 0000 000x |
| 0 | 0Ch | PIR1 | PSPIF(3) | ADIF | RCIF | TXIF | SSPIF | CCP1IF | TMR2IF | TMR1IF | 00000000 |
| 0 | 0Dh | PIR2 | – | – | – | EEIF | BCLIF | – | – | CCP2IF | -r-0 0–0 |
| 1 | 8Ch | PIE1 | PSPIE(2) | ADIE | RCIE | TXIE | SSPIE | CCP1IE | TMR2IE | TMR1IE | 00000000 |
| 1 | 8Dh | PIE2 | – | – | – | EEIE | BCLIE | – | – | CCP2IE | -r-0 0–0 |
The following paragraphs discuss the different register setting for interrupts
INTCON Register
The INTCON register is a readable and writable register, which contains various enable and flag bits for the TMR0 register overflow, RB port change and external RB0/INT pin interrupts.
| D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 |
| GIE | PEIE | TMR0IE | INTE | RBIE | TMR0IF | INTF | RBIF |
| Global Intr enable | Peripheral Interrupt Enable bit | TMR0 Overflow Interrupt Enable bit | RB0/INT External Interrupt Enable bit | RB Port Change Interrupt Enable bit | TMR0 Overflow Interrupt Flag bit | RB0/INT External Interrupt Flag bit | RB Port Change Interrupt Flag bit |
| 1-Enable
0-disable |
1-Enables
0-Disables |
1 Enable TMR0 intr
0 Disable |
1 enable
0 disable |
1 enable
0 disable |
1 TMR0 has overflowed | 1 interrupt occured | 1 = At least one of the RB7:RB4 pins changed state; a mismatch condition will continue to set the bit. Reading PORTB will end the mismatch condition and allow the bit to be cleared (must be cleared in software). 0 = None of the RB7:RB4 pins have changed state |
OPTION_REG
The OPTION_REG Register is a readable and writable register, which contains various control bits to configure the TMR0 prescaler/WDT postscaler (single assignable register known also as the prescaler), the external INT interrupt, TMR0 and the weak pull-ups on PORTB.
| D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 |
| RBPU’ | INTEDG | T0CS | T0SE | PSA | PS2 | PS1 | PS0 |
| PORTB Pull-up Enable bit | Interrupt Edge Select bit | TMR0 Clock Source Select bit
|
TMR0 Source Edge Select bit | Prescaler Assignment bit
|
Prescaler Rate Select bits | ||
| 1 Disable
0 enable by port latch |
1 Interrupt on rising edge of RB0/INT
0 on falling edge |
1 =Transition on T0CKI pin 0 = Internal instruction cycle clock (CLKO) |
1 = Increment on high-to-low transition on T0CKI pin 0 = Increment on low-to-high transition on T0CKI pin |
1 = Prescaler is assigned to the WDT 0 = Prescaler is assigned to the Timer0 module |
Note:There is only one prescaler available which is mutually exclusively shared between the T0 module and the WDT Timer. When assignment for the T0 module , then it is not for the Watchdog Timer and vice versa. This prescaler is not accessible but can be configured using PS2:PS0 bits of OPTION_REG. | ||
PIE1 Register
The PIE1 register contains the individual enable bits for the peripheral interrupts.
| D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 |
| PSPIE | ADIE | RCIE | TXIE | SSPIE | CCP1IE | TMR2IE | TMR1IE |
| Parallel Slave Port Read/Write Interrupt Enable bit | A/D Converter Interrupt Enable bit | USART Receive Interrupt Enable bit
|
USART Tx Interrupt Enable bit
|
Synchronous Serial Port Interrupt Enable bit | CCP1 Interrupt Enable bit | TMR2 to PR2 Match Interrupt Enable bit | TMR1 Overflow Interrupt Enable bit |
| 1 Enable
0 Disable |
1 Enable
0 Disable |
1 Enable
0 Disable |
1 Enable
0 Disable |
1 Enable
0 Disable |
1 Enable
0 Disable |
1 Enable
0 Disable |
1 Enable
0 Disable |
PIR Register
PIC microcontroller has two interrupt flag registers these are PIR1 and PIR2 registers. These flags are set or reset depending on the status of interrupt. Interrupt flag bits are set when an interrupt condition occurs regardless of the state of its corresponding enable bit or the global enable bit, GIE (INTCON<7>). User software should ensure the appropriate interrupt bits are clear prior to enabling an interrupt. These registers are explained in the following paragraphs.
| D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 |
| PSPIF | ADIF | RCIF | TXIF | SSPIF | CCP1IF | TMR2IF | TMR1IF |
| Parallel Slave Port Read/Write Interrupt Flag bit | A/D Converter Interrupt Flag bit | USART Receive Interrupt Flag bit | USART Transmit Interrupt Flag bit | Synchronous Serial Port (SSP) Interrupt Flag bit | CCP1 Interrupt Flag bit | TMR2 to PR2 Match Interrupt Flag bit | TMR1 Overflow Interrupt Flag bit
|
| ‘1’ READ/WRITE OPERATION IS COMPLETED
‘0’ Not Completed |
1-A/D conversion complete
‘0’ AD operation not completed |
1 =USART receive buffer is full
‘0’-Rx buffer empty |
1 =USART Tx buffer is empty
‘0’-USART Tx buffer full |
1 = TMR2 to PR2 match occurred
‘0’ No match |
1 = TMR1 register overflowed(must be cleared in s/w)
‘0’ no overflow |
PIE2 Register
The PIE2 register contains the individual enable bits forthe CCP2 peripheral interrupt, the SSP bus collision interrupt, EEPROM write operation interrupt and the comparator interrupt.
| D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 |
| – | CMIE | – | EEIE | BCLIE | – | – | CCP2IE |
| – | Comparator Interrupt Enable bit | – | EEPROM Write Operation Interrupt Enable bit | Bus Collision Interrupt Enable bit | – | – | CCP2 Interrupt Enable bit |
| 1 = Enables
‘0’ Disable |
1 = Enable
‘0’ Disable |
1 = Enable
‘0’ Disable |
1 = Enable
‘0’ Disable |
PIR2 Register
The PIR2 register contains the flag bits for the CCP2 interrupt, the SSP bus collision interrupt, EEPROM write operation interrupt and the comparator interrupt.
| D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 |
| – | CMIF | – | EEIF | BCLIF | – | – | CCP2IF |
| Comparator Interrupt Flag bit | EEPROM Write Operation Interrupt Flag bit | Bus Collision Interrupt Flag bit
|
CCP2 Interrupt Flag bit
|
||||
| 1 = The comparator input has changed (must be cleared in software)
‘0’ No change |
‘1’ operation complete
‘0’ operation not yet completed |
‘1’ A bus collision has occurred in the SSP when configured for I2C Master mode
‘0’ No collision |