Datasheet

Product data sheet Rev. 6 — 11 July 2013 58 of 86

NXP Semiconductors

PCF2127AT

Integrated RTC, TCXO and quartz crystal

Table 59. Command byte definition

Bit Symbol Value Description

7R/W

data read or write selection

0 write data

1 read data

6 to 5 SA 01 subaddress;

other codes will cause the device to ignore data

transfer

4 to 0 RA 00h to 1Dh register address

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

Fig 36. SPI-bus write example

001aaj348

seconds data 45

BCD

minutes data 10

BCD

addr 03hR/W

03xx 04 05

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 I

currents may result.

Fig 37. SPI-bus read example

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months data 11

BCD

years data 06

BCD

addr 08hR/W

08xx 09 0A

SCL

SDI

SDA/CE

address

counter

SDO