A low-power CMOS real-time clock and calendar with an I2C interface, in SO-8, one of the most common RTCs after the DS series. It keeps seconds through years with automatic leap-year handling from a 32.768 kHz crystal on OSCI/OSCO, and adds a programmable alarm, a countdown timer, a programmable clock output (CLKOUT), and a low-voltage detector, all of which raise the open-drain INT pin so the host is interrupted rather than polling. Bus speed is up to 400 kbit/s. Its very low timekeeping current suits coin-cell backup. Runs 1.0-5.5 V.

Pinout

Pin	Name	Type	Function
1	OSCI	input	Oscillator input. Connect one terminal of the 32.768 kHz quartz crystal here. The device has an integrated oscillator capacitor (C_OSCO) so typically only the crystal is required between OSCI and OSCO.
2	OSCO	output	Oscillator output. Connect the other terminal of the 32.768 kHz quartz crystal here. Together with OSCI drives the on-chip oscillator that clocks the RTC.
3	INT	output	Interrupt output, open-drain, active LOW. Signals alarm and timer events; requires an external pull-up resistor to VDD.
4	VSS	power_in	Ground (0 V) reference for the device.
5	SDA	bidirectional	I2C-bus serial data input/output (open-drain). Requires external pull-up. Bus operates up to 400 kbit/s at VDD = 1.8 V to 5.5 V. Target address: A2h (write) / A3h (read).
6	SCL	input	I2C-bus serial clock input. Requires external pull-up. Maximum 400 kHz.
7	CLKOUT	output	Programmable square-wave clock output (open-drain). Selectable 32.768 kHz (default), 1.024 kHz, 32 Hz, or 1 Hz via CLKOUT_control register (0Dh). High-impedance when disabled; requires an external pull-up when used.
8	VDD	power_in	Supply voltage. Clock operates 1.0 V to 5.5 V (at room temperature); I2C-bus operation requires 1.8 V to 5.5 V. Typical backup current 0.25 μA at 3.0 V, 25 °C.

Key specifications

Parameter	Value
Type	I2C real-time clock/calendar
Timekeeping	seconds to year, BCD, leap-year
Extras	alarm + countdown timer + CLKOUT
Interrupt	open-drain INT (alarm/timer/LVD)
Bus	I2C up to 400 kbit/s
Timebase	32.768 kHz crystal (OSCI/OSCO)
Supply voltage	1.0-5.5 V
Package	SO-8

Ordering variants

Same part, different packaging or reel option.

PCF8563T/5,518 (SO-8)
PCF8563TS (TSSOP-8)

CAD (KiCad official)

Symbol: Timer_RTC:PCF8563T
Footprint: Package_SO:SOIC-8_3.9x4.9mm_P1.27mm
3D model: SOIC-8 (KiCad packages3D)

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: NXP Semiconductors datasheet (50 pp, sha256 2ed5d1b0a1051d0e, retrieved 2026-08-17, tier: manufacturer)
Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF