PCF2127ATSLASH1 datasheet(56/80 Pages) NXP

56 / 80 page

PCF2127A_2

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Product data sheet

Rev. 02 — 7 May 2010

56 of 80

NXP Semiconductors

PCF2127A

Integrated RTC, TCXO and quartz crystal

Table 58.

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

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

Fig 36. SPI-bus write example

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seconds data 45BCD

minutes data 10BCD

addr 03h

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 37. SPI-bus read example

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months data 11BCD

years data 06BCD

addr 08h

R/W

SCL

SDI

SDA/CE

address

counter

SDO

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