SI5338 SILABS [Silicon Laboratories], SI5338 Datasheet - Page 28

• Manufacturer Part Number: SI5338
• Description: I2C-PROGRAMMABLE ANY-FREQUENCY, ANY-OUTPUT QUAD CLOCK GENERATOR
• Manufacturer: SILABS [Silicon Laboratories]

Si5338
6. Si5338 Registers
This section describes the registers and their usage in
detail. These values are easily configured using
ClockBuilder Desktop (see "3.1.1. ClockBuilder™
Desktop Software" on page 16). See AN428 for a
working example using Silicon Labs' F301 MCU.
6.1. Register Write-Allowed Mask
The masks listed in Table 15 indicate which bits in each
register of the Si5338 can be modified and which bits
cannot. Therefore, these masks are write-allowed or
write-enabled bits. These masks must be used to
perform a read-modify-write on each register.
If a mask is 0x00, all bits in the associated register are
reserved and must remain unchanged. If the mask is
28
// ignore registers with masks of 0x00
if(mask != 0x00){
}
if(mask == 0xFF){
} else {
}
// do a regular I2C write to the register
// at addr with the desired data value
write_Si5338(addr, data);
// do a read-modify-write using I2C and
// bit-wise operations
// get the current value from the device at the
// register located at addr
curr_val = read_Si5338(addr);
// clear the bits that are allowed to be
// accessed in the current value of the register
clear_curr_val = curr_val AND (NOT mask);
// clear the bits in the desired data that
// are not allowed to be accessed
clear_new_val = data AND mask;
// combine the cleared values to get the new
// value to write to the desired register
combined = clear_curr_val OR clear_new_val;
write_Si5338(addr, combined);
Rev. 0.6
0xFF, all the bits in the register can be changed. All
other registers require a read-modify-write procedure to
write to the registers. ClockBuilder Desktop can be used
to create ANSI C code (Options  Save C code header
file) with the register contents and mask values. AN428
demonstrates the usage of this header file and the read-
modify-write procedure.
The following code demonstrates the application of the
above write allowed mask.



Let addr be the address of the register to access.
Let data be the data or value to write to the register
located at addr.
Let mask be the write-allowed bits defined for the
corresponding register.