Philips Semiconductors
PCF8563
Real-time clock/calendar
Product specification 16 April 1999 4 of 30
9397 750 04855
© Philips Electronics N.V. 1999. All rights reserved.
8. Functional description
The PCF8563 contains sixteen 8-bit registers with an auto-incrementing address
register, an on-chip 32.768 kHz oscillator with an integrated capacitor, a frequency
divider which provides the source clock for the Real-Time Clock (RTC), a
programmable clock output, a timer, an alarm, a voltage-low detector and a 400 kHz
I
2
C-bus interface.
All 16 registers are designed as addressable 8-bit parallel registers although not all
bits are implemented. The first two registers (memory address 00H and 01H) are
used as control and/or status registers. The memory addresses 02H through 08H are
used as counters for the clock function (seconds up to year counters). Address
locations 09H through 0CH contain alarm registers which define the conditions for an
alarm. Address 0DH controls the CLKOUT output frequency. 0EH and 0FH are the
timer control and timer registers, respectively.
The Seconds, Minutes, Hours, Days, Months, Years as well as the Minute alarm,
Hour alarm and Day alarm registers are all coded in BCD format. The Weekdays and
Weekday alarm register are not coded in BCD format.
When one of the RTC registers is read the contents of all counters are frozen.
Therefore, faulty reading of the clock/calendar during a carry condition is prevented.
8.1 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.
8.2 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 Tabl e 7). The timer flag TF can
only be cleared by software. The asserted timer flag TF can be used to generate an
interrupt (INT). The interrupt may be generated as a pulsed signal every countdown
period or as a permanently active signal which follows the condition of TF. TI/TP (see
Table 7) is used to control this mode selection. When reading the timer, the current
countdown value is returned.
8.3 CLKOUT output
A programmable square wave is available at the CLKOUT pin. Operation is controlled
by the CLKOUT frequency register (address 0DH; see Tabl e 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.
