NEC PD750008 - Manual (Page 125)

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CHAPTER 5 PERIPHERAL HARDWARE FUNCTIONS
MOV XA, BC
MOV BUFF, XA ; Store data
SET1 FLAG ; Set data presence flag
RETI
5.4 CLOCK TIMER
The µPD750008 contains one clock timer, which has the following functions.
(a) The clock timer sets the test flag (IRQW) every 0.5 seconds.
The IRQW can release the standby mode.
(b) Either the main system clock or the subsystem clock can be used to produce 0.5-second intervals.
Use a main system clock of 4.194304 MHz.
(c) The fast-forward mode produces an interval 128 times faster (3.91 ms), which is useful for program
debugging and testing.
(d) Any of the frequencies 2.048 kHz, 4.096 kHz, and 32.768 kHz can be output to the P23/BUZ pin, so
that it can be used for sounding the buzzer and for system clock frequency trimming.
(e) The frequency divider can be cleared to start the clock from zero second.