CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (FSK Demodulator)

The interrupt factor flag is reset to "0" by writing "1".

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.

At initial reset, these flags are set to "0".

4.15.6 Programming notes

(1)When starting the FSK demodulator operation, the OSC3 oscillation circuit must be turned ON and the CPU operating clock must be switched to the OSC3 clock.

The OSC3 oscillation circuit takes a maximum 5 msec for oscillation stabilization after turning the circuit ON. Consequently, allow an adequate waiting time after turning ON the OSC3 oscillation, before starting the FSK operation. Note that the oscillation start time will vary somewhat depending on the oscillator and on the externally attached parts.

(2)In order to decrease current consumption, the FSK demodulator and the OSC3 oscillation circuit should be turned OFF when their operations are not necessary.

(3)When detecting a carrier, the FSK demodulator may output invalid data at the rising edge of the CDET signal. In this case, the first byte received to the serial interface (2) may result in a parity error or a framing error. As this byte is generally used as a leader code, ignore the error in the processing.

(4)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.

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S1C63558 TECHNICAL MANUAL