External Interrupts
Can interrupt using the INT0 or INT1 pins (port 3: pin 2,3)
- Interrupt on level or falling edge of signal (TCON specifies which)
- Pin is sampled once every 12 clock cycles
- for interrupt on edge, signal must be high 12 cycles, low 12 cycles
- Response time takes at least 3 instuctions cycles
- 1 to sample
- 2 for call to interrupt routine
- more if a long instruction is in progress (up to 6 more)
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