Si5351A/B/C
16 Preliminary Rev. 0.95
5. Configuring the Si5351
The Si5351 is a highly flexible clock generator which is entirely configurable through its I
2
C interface. The device’s
default configuration is stored in non-volatile memory (NVM) as shown in Figure 11. The NVM is a one time
programmable memory (OTP) which can store a custom user configuration at power-up. This is a useful feature for
applications that need a clock present at power-up (e.g., for providing a clock to a processor).
Figure 11. Si5351 Memory Configuration
During a power cycle the contents of the NVM are copied into random access memory (RAM), which sets the
device configuration that will be used during normal operation. Any changes to the device configuration after
power-up are made by reading and writing to registers in the RAM space through the I
2
C interface. A detailed
register map is shown in Section "8. Register Descriptions" on page 25.
5.1. Writing a Custom Configuration to RAM
To simplify device configuration, Silicon Labs has released the ClockBuilder Desktop. The software serves two
purposes: to configure the Si5351 with optimal configuration based on the desired frequencies and to control the
EVB when connected to a host PC.
The optimal configuration can be saved from the software in text files that can be used in any system, which
configures the device over I
2
C. ClockBuilder Desktop can be downloaded from www.silabs.com/ClockBuilder and
runs on Windows XP, Windows Vista, and Windows 7.
Once the configuration file has been saved, the device can be programmed via I
2
C by following the steps shown in
Figure 12.
Power-Up
I
2
C
RAM
NVM
(OTP)
Default
Config
