PIC16C71X
8.5.1
INT INTERRUPT
8.5.2
TMR0 INTERRUPT
External interrupt on RB0/INT pin is edge triggered:
either rising if bit INTEDG (OPTION<6>) is set, or fall-
ing, if the INTEDG bit is clear. When a valid edge
appears on the RB0/INT pin, flag bit INTF
(INTCON<1>) is set. This interrupt can be disabled by
clearing enable bit INTE (INTCON<4>). Flag bit INTF
must be cleared in software in the interrupt service rou-
tine before re-enabling 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 inter-
rupt enable bit GIE decides whether or not the proces-
sor branches to the interrupt vector following wake-up.
See Section 8.8 for details on SLEEP mode.
An overflow (FFh → 00h) in the TMR0 register will set
flag bit T0IF (INTCON<2>). The interrupt can be
enabled/disabled by setting/clearing enable bit T0IE
(INTCON<5>). (Section 6.0)
8.5.3
PORTB INTCON CHANGE
An input change on PORTB<7:4> sets flag bit RBIF
(INTCON<0>). The interrupt can be enabled/disabled
by setting/clearing enable bit RBIE (INTCON<4>).
(Section 5.2)
Note: For the PIC16C71
if a change on the I/O pin should occur
when the read operation is being executed
(start of the Q2 cycle), then the RBIF inter-
rupt flag may not get set.
FIGURE 8-19: INT PIN INTERRUPT TIMING
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
OSC1
CLKOUT
3
4
INT pin
1
1
Interrupt Latency
INTF flag
(INTCON<1>)
5
2
GIE bit
(INTCON<7>)
INSTRUCTION FLOW
PC
0004h
PC+1
PC+1
—
0005h
PC
Instruction
fetched
Inst (PC)
Inst (PC+1)
Inst (0004h)
Inst (0005h)
Inst (0004h)
Instruction
executed
Dummy Cycle
Dummy Cycle
Inst (PC)
Inst (PC-1)
Note
1: INTF flag is sampled here (every Q1).
2: Interrupt latency = 3-4 Tcy where Tcy = instruction cycle time.
Latency is the same whether Inst (PC) is a single cycle or a 2-cycle instruction.
3: CLKOUT is available only in RC oscillator mode.
4: For minimum width of INT pulse, refer to AC specs.
5: INTF is enabled to be set anytime during the Q4-Q1 cycles.
1997 Microchip Technology Inc.
DS30272A-page 63
MICROCHIP [ MICROCHIP ]
