sx1441 Semtech Corporation, sx1441 Datasheet - Page 24

• Manufacturer Part Number: sx1441
• Description: Bluetooth V1.2 Soc For Voice And Data Applications With Dsp Capabilities
• Manufacturer: Semtech Corporation

Personal Area Network
The high prescaler output may be used as the low prescaler input. A decoder is used to select from the high
prescaler the frequency tap that is the closest to 32 kHz to operate the low prescaler when SLW_CLOCK_IN is not
running. In this case, the RC oscillator frequency will also be valid for the low prescaler frequency outputs.
The Table 24 shows how the RC trimming values in the RegSysRcTrim1 and RegSysRcTrim2 registers are
decoded to select the input frequency from the high prescaler. The least significant bits of the RCFine word are
ignored.
In order to ensure the correct frequency selection for the low prescaler with an external clock, a proper value must
be set in the RC trim registers. If the frequency is not set correctly, all timings derived from the low prescaler will be
shifted accordingly (e.g. watchdog and interrupt frequencies).
In the Table 24, ckRCext stands for either ckRC or SYS_CLOCK_IN.
© Semtech 2006
RCCoarseMSB &
RCCoarseLSB &
RCDivFactor &
Decoder
[0x0000]hex
[0x0002]hex
[0x0100]hex
[0x0102]hex
[0x010a]hex
[0x0110]hex
[0x0119]hex
[0x0120]hex
[0x0127]hex
[0x0130]hex
RCFine
SLW_CLOCK_IN
Selected high
prescaler tap
ckRCext / 128
ckRCext / 128
ckRCext / 128
ckRCext / 128
ckRCext / 64
ckRCext / 32
ckRCext / 64
ckRCext / 64
ckRCext / 64
ckRCext / 64
SelLowPresIn
Figure 13 - Low prescaler block diagram
1
0
÷ 2
÷ 2
÷ 2
÷ 2
÷ 2
÷ 2
÷ 2
24
Ck32kHz
Ck16kHz
Ck8kHz
Ck4kHz
Ck2kHz
Ck1kHz
Ck512Hz
Ck256Hz
RCCoarseMSB &
RCCoarseLSB &
RCDivFactor &
[0x04d0]hex
[0x04d6]hex
[0x04e0]hex
[0x04e5]hex
[0x0500]hex
[0x0502]hex
[0x050a]hex
[0x04c8]hex
[0x04f0]hex
[0x04f3]hex
RCFine
÷ 2
÷ 2
÷ 2
÷ 2
÷ 2
÷ 2
÷ 2
÷ 2
SX1441 – Bluetooth® 1.2 SoC
Selected high
prescaler tap
ckRCext / 32
ckRCext / 16
ckRCext / 32
ckRCext / 16
ckRCext / 32
ckRCext / 16
ckRCext / 32
ckRCext / 2
ckRCext / 4
ckRCext / 8
Ck128Hz
Ck64Hz
Ck32Hz
Ck16Hz
Ck8Hz
Ck4Hz
Ck2Hz
Ck1Hz
www.semtech.com
Data Sheet