Si5345-44-42-D-RM
16
Rev. 1.0
4.2. Dynamic PLL Changes
4.2.1. Revision B and A
It is possible for a PLL to become unresponsive (i.e., lose lock indefinitely) when it is dynamically reprogrammed or
changed via the serial port. Reprogramming/changing the N divider does not affect the PLL. Any change that
causes the VCO frequency to change by more than 250 ppm since Power-up, NVM download, or SOFT_RST
requires the following special sequence of writes. Changes to the following registers require the following special
sequence of writes:
XAXB_FREQ_OFFSET
PXAXB
MXAXB_NUM
MXAXB_DEN
M_NUM
M_DEN
1. |First, the preamble
Write 0x0B24 = 0xD8
Write 0x0B25 = 0x00
2. Wait 300 ms.
3. Then perform the desired register modifications
4. Write SOFT_RST - x001C[0] = 1
5. Write the post-amble
Write 0x0B24 = 0xDB
Write 0x0B25 = 0x02
4.2.2. Revision D
The revision D preamble and postamble values for updating certain registers during device operation have
changed after revision B. Either the new or old values below may be written to revision D or later devices without
issue. No system software changes are necessary for legacy systems. When writing old values, note that reading
back these registers will not give the written old values, but will reflect the new values. Silicon Labs recommends
using the new values for all revision D and later designs, since the write and read values will match.
The device revision can be determined in the setting DEVICE_REV, register 0x0005.
DEVICE_REV = 0x02 or higher: New Values
Revision
D
Preamble:0x0B24 =
0xC0
, 0x0B25 = 0x00
Revision
D
Postamble:0x0B24 =
0xC3
, 0x0B25 = 0x02
Note that revision B and earlier devices must continue to use the original values for these registers:
DEVICE_REV = 0x00 or 0x01: Old Values
Revision
B
Preamble:0x0B24 =
0xD8
, 0x0B25 = 0x00
Revision
B
Postamble:0x0B24 =
0xDB
, 0x0B25 = 0x02