Sony IT-M708 Operation Manual page 22

KEY SCAN TIMING
Following chart shows a state in case that the key which connected with KEY SCAN 0(KS 0/P50)
and KEY IN 0(KI 0/P40)is depressed.
KEY SCAN is not implemented in IDLE state, and all SCAN ports turn to ACTIV then observes
the key is depressed. (Which key is depressed is unknown if SCAN is not implemented.)
If input by any key is detected in 15mS TIMER INTERRUPTION time, KEY SCAN is
implemented for 1mS INTERRUPTION time and detects which key is depressed.
SCAN is LOW ACTIVE.
IF it is detected that same key is depressed two times successively for 30mS, it is presumed the
key is depressed.
key input detection
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