NXP Semiconductors PCA8565, PCF85x3, PCF2123, PCA2125 Application diagram 1, I2C-bus interface

NXP Semiconductors	UM10301
	User Manual PCF85x3, PCA8565 and PCF2123, PCA2125

1 F 100 nF

VDD

SCL

CLOCK CALENDAR

OSCI PCF8563

SDA

OSCO VSS

		VDD
SDA
		MASTER
	TRANSMITTER/
SCL	RECEIVER
VDD
R	R	R: pull-up resistor
		tr
		R =
		Cb

SDA SCL

(I2C-bus) mgm665

Fig 18. Application diagram 1, I2C-bus interface

The following example is with PCA2125 and SPI interface.

1 F
supercapacitor
100 nF
OSCI	VDD	CLKOUT	CE
	PCA2125		SCL
OSCO			SDI
			SDO
INT		VSS

001aaf918

The 1 Farad capacitor is used as a standby/backup supply. With the RTC in its minimum power configuration i.e. timer off and CLKOUT off, the RTC may operate for several months.

Fig 19. Application diagram 2, SPI interface

Remark: CLKOUT and INT are open drain outputs. If a pull-up resistor is used, it should not be connected to voltages higher than the maximum operating voltage as specified for the RTC. If the outputs need to be used to switch signals connected to a higher potential, it is necessary to use an external transistor.

UM10301_1		© NXP B.V. 2008. All rights reserved.
User manual	Rev. 01 — 23 December 2008	42 of 52