pcf2127a NXP Semiconductors, pcf2127a Datasheet - Page 54

• Manufacturer Part Number: pcf2127a
• Description: Integrated Rtc, Tcxo And Quartz Crystal
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCF2127A_1
Product data sheet
9.1.1 Data transmission
9.1 SPI-bus interface
Data transfer to and from the device is made via a 3 wire SPI-bus (see
lines for input and output are split. The data input and output line can be connected
together to facilitate a bidirectional data bus (see
The SPI-bus is initialized whenever the chip enable line pin CE is inactive.
Table 57.
[1]
The chip enable signal is used to identify the transmitted data. Each data transfer is a
byte, with the Most Significant Bit (MSB) sent first.
The transmission is controlled by the active LOW chip enable signal SDA/CE. The first
byte transmitted is the command byte. Subsequent bytes will be either data to be written
or data to be read (see
The command byte defines the address of the first register to be accessed and the
read/write mode. The address counter will auto increment after every access and will
reset to zero after the last valid register is accessed. The read/write bit (R/W) defines if the
following bytes will be read or write information.
Symbol
SDA/CE
SCL
SDI
SDO
Fig 34. SDI, SDO configurations
Fig 35. Data transfer overview
The chip enable must not be wired permanently LOW.
Serial interface
data bus
Function
chip enable input;
active LOW
serial clock input
serial data input
serial data output
CE
Rev. 01 — 21 January 2010
Figure
COMMAND
35).
two wire mode
SDO
SDI
DATA
[1]
Description
when HIGH, the interface is reset;
when CE is HIGH, input may float;
when CE is HIGH, input may float;
push-pull output;
input may be higher than V
input may be higher than V
input may be higher than V
input data is sampled on the rising edge of SCL
drives from V
output data is changed on the falling edge of SCL
Integrated RTC, TCXO and quartz crystal
single wire mode
SDO
SDI
DATA
Figure
001aai560
34).
SS
to V
BBS
DATA
;
PCF2127A
DD
DD
DD
Table
© NXP B.V. 2010. All rights reserved.
;
001aaj347
57). The data
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