• 4 •

2.2 Alarm function modes

By clearing the MSB (bit

———

AE = Alarm Enable) of one or more of the alarm registers, the

corresponding alarm condition(s) will be active. In this way an alarm can be generated from

once per minute up to once per week. The alarm condition sets the alarm flag, AF (bit 3 of

Control/Status 2 register). The asserted AF can be used to generate an interrupt (INT). Bit AF

can only be cleared by software.

2.3 Timer

The 8-bit countdown timer (address 0FH) is controlled by the Timer Control register

(address 0EH; see Table 25). The Timer Control register selects one of 4 source clock

frequencies for the timer (4096, 64, 1, or 1⁄60 Hz), and enables/disables the timer. The timer

counts down from a software-loaded 8-bit binary value. At the end of every countdown, the

timer sets the timer flag TF (see Table 7). The timer flag TF can only be cleared by software.

The asserted timer flag TF can be used to generate aninterrupt (INT). The interrupt may be

generated as a pulsed signal every countdownperiod or as a permanently active signal which

follows the condition of TF. TI/TP (seeTable 7) is used to control this mode selection. When

reading the timer, current countdown value is returned.

2.4 CLKOUT output

A programmable square wave is available at the CLKOUT pin. Operation is controlled by

the CLKOUT frequency register (address 0DH; see Table 23). Frequencies of 32.768 kHz

(default), 1024, 32 and 1 Hz can be generated for use as a system clock, microcontroller clock,

input to a charge pump, or for calibration of the oscillator. CLKOUT is an open-drain output

and enabled at power-on. If disabled it becomes high-impedance.

2.5 Reset

HM8563 includes an internal reset circuit which is active whenever the oscillator is

pointer, are cleared with the exception of bits FE, VL, TD1, TD0, TESTC and

———

AEwhich are set

to logic 1.

2.6 Voltage-low detector

(Voltage Low, bit 7 in the Seconds register) is set to indicate that reliable clock/calendar

information is no longer guaranteed. The VL flag can only be cleared by software.

be set. This will indicate that the time may have been corrupted.

HM8563