NXP Semiconductors PCF2123, PCF85x3, PCA8565 Register overview PCF8563, Address Register name Bit

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

In BCD every digit of the decimal system is represented by a 4-bit group. For example: 15710 = 0001 0101 0111BCD

This is not the same as binary representation. It is clear that BCD is not the most efficient way of coding since every 4-bit group (nibble) could represent numbers 0 through 15, but in BCD never represents numbers bigger than 9. But for some applications it is convenient to use BCD and real time clocks are one such application.

Each 8-bit register contains two digits each represented by one nibble. Each 4-bit nibble can represent the value of 0 up to 9 in BCD, but for some digits the maximum value to be represented will be lower. The minute register for example will never have to count higher than 59. The upper most digit can here be represented by 3 bits, freeing up one bit that can be used to indicate something else.

Not all NXP real-time clocks have exactly the same register implementation and thus the datasheet of the particular device should be consulted. As an example the register organization of the PCF8563 is given below. Note that this is just one example and that register organization of other types is not necessarily exactly the same.

Table 1. Register overview PCF8563

Bit positions labelled as x are not implemented. When setting a register, also a value must be written for the ‘x’ bit positions. When these are read back, the read back values may differ from what was previously written.

Bit positions labelled with 0 should always be written with logic 0; if read they could be either logic 0 or logic 1.

Address	Register name	Bit 7	Bit 6	Bit 5		Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
00HEX	control / status 1	TEST1	0	STOP	0		TESTC	0	0	0
01HEX	control / status 2	0	0	0		TI/TP	AF	TF	AIE	TIE
02HEX	seconds	VL			<seconds 00 to 59 coded in BCD>
03HEX	minutes	x			<minutes 00 to 59 coded in BCD>
04HEX	hours	x	x			<hours 00 to 23 coded in BCD>
05HEX	days	x	x			<days 01 to 31 coded in BCD>
06HEX	weekdays	x	x	x		x	x		<weekdays 0 to 6>
07HEX	months / century	C	x	x			<months 01 to 12 coded in BCD>
08HEX	years			<years 00 to 99 coded in BCD>
09HEX	minute alarm	AE			<minute alarm 00 to 59 coded in BCD>
0AHEX	hour alarm	AE	x			<hour alarm 00 to 23 coded in BCD>
0BHEX	day alarm	AE	x			<day alarm 01 to 31 coded in BCD>
0CHEX	weekday alarm	AE	x	x		x	x	<weekday alarm 0 to 6>
0DHEX	CLKOUT control	FE	x	x		x	x	x	FD1	FD0
0EHEX	timer control	TE	x	x		x	x	x	TD1	TD0
0FHEX	timer				<timer countdown value>

UM10301_1		© NXP B.V. 2008. All rights reserved.
User manual	Rev. 01 — 23 December 2008	5 of 52