Datasheet
PCF8523 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 6 — 17 September 2013 32 of 78
NXP Semiconductors
PCF8523
Real-Time Clock (RTC) and calendar
8.9.1 Timer registers
8.9.1.1 Register Tmr_CLKOUT_ctrl and clock output
[1] Default value.
8.9.1.2 CLKOUT frequency selection
Clock output operation is controlled by the COF[2:0] in the Tmr_CLKOUT_ctrl register.
Frequencies of 32.768 kHz (default) down to 1 Hz can be generated (see Table 35
) for
use as a system clock, microcontroller clock, input to a charge pump, or for calibration of
the oscillator.
A programmable square wave is available at pin INT1
/CLKOUT and pin CLKOUT, which
are both open-drain outputs. Pin INT1
/CLKOUT has both functions of INT1 and CLKOUT
combined.
The duty cycle of the selected clock is not controlled but due to the nature of the clock
generation, all clock frequencies except 32.768 kHz have a duty cycle of 50 : 50.
The STOP bit function can also affect the CLKOUT signal, depending on the selected
frequency. When STOP is active, the INT1
/CLKOUT and CLKOUT pins are
high-impedance for all frequencies except of 32.768 kHz, 16.384 kHz and 8.192 kHz. For
more details, see Section 8.10
.
Table 34. Tmr_CLKOUT_ctrl - timer and CLKOUT control register (address 0Fh) bit
description
Bit Symbol Value Description
7TAM 0
[1]
permanent active interrupt for timer A and for
the second interrupt timer
1 pulsed interrupt for timer A and the second
interrupt timer
6TBM 0
[1]
permanent active interrupt for timer B
1 pulsed interrupt for timer B
5 to 3 COF[2:0] see Table 35
CLKOUT frequency selection
2 to 1 TAC[1:0] 00
[1]
to 11 timer A is disabled
01 timer A is configured as countdown timer
if CTAIE (register Control_2) is set logic 1, the
interrupt is activated when the countdown
timed out
10 timer A is configured as watchdog timer
if WTAIE (register Control_2) is set logic 1,
the interrupt is activated when timed out
0TBC 0
[1]
timer B is disabled
1 timer B is enabled
if CTBIE (register Control_2) is set logic 1, the
interrupt is activated when the countdown
timed out