PCF2129AT datasheet(46/68 Pages) NXP

46 / 68 page

PCF2129A_1

Product data sheet

Rev. 01 — 13 January 2010

46 of 68

NXP Semiconductors

PCF2129A

Integrated RTC, TCXO and quartz crystal

Table 49.

Command byte definition

Bit

Symbol

Value

Description

7R/W

data read or write selection

write data

read data

6 to 5

subaddress;

other codes will cause the device to ignore data

transfer

4 to 0

00h to 1Dh register address range

In this example, the register Seconds is set to 45 seconds and the register Minutes to 10 minutes.

Fig 29. SPI-bus write example

001aaj348

seconds data 45BCD

minutes data 10BCD

addr 34bin

R/W

SCL

SDI

SDA/CE

address

counter

In this example, the registers Months and Years are read. The pins SDI and SDO are not connected together. For this

configuration, it is important that pin SDI is never left floating. It must always be driven either HIGH or LOW. If pin SDI is left

open, high IDD currents may result.

Fig 30. SPI-bus read example

001aaj349

months data 11BCD

years data 06BCD

addr 34bin

R/W

SCL

SDI

SDA/CE

address

counter

SDO

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