PCF8563
NXP Semiconductors
Real-time clock/calendar
8.7 Register CLKOUT_control and clock output
Frequencies of 32.768 kHz (default), 1.024 kHz, 32 Hz, 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.
Table 22. CLKOUT_control - CLKOUT control register (address 0Dh) bit description
Bit
Symbol
Value
Description
7
FE
0
the CLKOUT output is inhibited and CLKOUT output is
set high-impedance
1[1]
-
the CLKOUT output is activated
6 to 2 -
unused
1 to 0 FD[1:0]
frequency output at pin CLKOUT
00[1]
01
32.768 kHz
1.024 kHz
32 Hz
10
11
1 Hz
[1] Default value.
8.8 Timer function
The 8-bit countdown timer at address 0Fh is controlled by the Timer_control register at
address 0Eh. The Timer_control register determines one of 4 source clock frequencies for
the timer (4096 Hz, 64 Hz, 1 Hz, or 1⁄60 Hz), and enables or 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 TF may only be cleared by using the interface. The
asserted TF can be used to generate an interrupt on pin INT. The interrupt may be
generated as a pulsed signal every countdown period or as a permanently active signal
which follows the state of TF. Bit TI_TP is used to control this mode selection. When
reading the timer, the current countdown value is returned.
8.8.1 Register Timer_control
Table 23. Timer_control - timer control register (address 0Eh) bit description
Bit
Symbol
Value
Description
7
TE
0[1]
timer is disabled
timer is enabled
unused
1
6 to 2 -
-
1 to 0 TD[1:0]
timer source clock frequency select[2]
00
4.096 kHz
01
64 Hz
10
1 Hz
1
11[2]
⁄60 Hz
[1] Default value.
[2] These bits determine the source clock for the countdown timer; when not in use, TD[1:0] should be set to
1
⁄60 Hz for power saving.
PCF8563
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© NXP B.V. 2012. All rights reserved.
Product data sheet
Rev. 10 — 3 April 2012
17 of 50
NXP [ NXP ]
