Datasheet

PCF2129 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 7 — 19 December 2014 51 of 86
NXP Semiconductors
PCF2129
Accurate RTC with integrated quartz crystal for industrial applications
9. Interfaces
The PCF2129 has an I
2
C-bus or SPI-bus interface using the same pins. The selection is
done using the interface selection pin IFS (see Table 74
).
9.1 SPI-bus interface
Data transfer to and from the device is made by a 3 line SPI-bus (see Table 75). The data
lines for input and output are split. The data input and output line can be connected
together to facilitate a bidirectional data bus (see Figure 29
). The SPI-bus is initialized
whenever the chip enable line pin SDA/CE
is inactive.
Table 74. Interface selection input pin IFS
Pin Connection Bus interface Reference
IFS V
SS
SPI-bus Section 9.1
BBS I
2
C-bus Section 9.2
To select the SPI-bus interface, pin IFS has to be
connected to pin V
SS
.
To select the I
2
C-bus interface, pin IFS has to be
connected to pin BBS.
a. SPI-bus interface selection b. I
2
C-bus interface selection
Fig 28. Interface selection
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Fig 29. SDI, SDO configurations
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