Epson S1C63666 Technical Manual page 51

4.5.5 Programming notes
(1) When input ports are changed from high to low by pull-down resistors, the fall of the waveform is
delayed on account of the time constant of the pull-down resistor and input gate capacitance. Hence,
when fetching input ports, set an appropriate waiting time.
Particular care needs to be taken of the key scan during key matrix configuration.
Make this waiting time the amount of time or more calculated by the following expression.
10 × C × R
C: terminal capacitance 5 pF + parasitic capacitance ? pF
R: pull-down resistance 375 kΩ (Max.)
(2) After an interrupt occurs, the same interrupt will occur again if the interrupt enabled state (I flag =
"1") is set or the RETI instruction is executed unless the interrupt factor flag is reset. Therefore, be sure
to reset (write "1" to) the interrupt factor flag in the interrupt service routine before shifting to the
interrupt enabled state.
S1C63666 TECHNICAL MANUAL
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Input Ports)
EPSON
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