PCF8563

8/23

APPLICATION SUMMARY

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

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.

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.

Timer

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

(address 0EH). 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. 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 is used to control this mode selection. When reading the timer, the

current countdown value is returned.