
UM10850
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2016. All rights reserved.
User manual
Rev. 2.4 — 13 September 2016
52 of 464
NXP Semiconductors
UM10850
Chapter 4: LPC5410x System configuration (SYSCON)
else if (M >=60) then
SELI = 4*(1024/(M+9))
else
SELI = (M & 0x3C) + 4; /* & denotes bitwise AND */
SELR = 0;
Remark:
If the 32 kHz RTC oscillator is used as the reference input to the PLL, then use
fixed values SELI=1, SELP=6, and SELR=0, instead of applying the above rules. These
values reduce the PLL loop bandwidth to combat the effect of reference oscillator jitter on
the PLL output signal.
Remark:
The values for SELP, SELI, and SELR are generated by the encoding block
when the spread spectrum clock generator is enabled and need not be programmed
explicitly.
Remark:
While the PLL0 output is in use, do not change the MDEC value. Changing the
MDEC value changes the FCCO frequency and can cause the system to fail.
4.5.37.5.2
System PLL spread spectrum control register 1
Table 71.
System PLL spread spectrum control register 1 (SYSPLLSSCTRL1, address 0x4000 01C4) bit description
Bit
Symbol
Value
Description
Reset
value
18:0
MD
M- divider value with fraction.
MD[18:11]: integer portion of the feedback divider value.
MD[10:0]: fractional portion of the feedback divider value.
0
19
MDREQ
MD reload request. When a 1 is written to this bit, the MD value is loaded into the PLL.
This bit is cleared when the load is complete.
0
22:20
MF
Programmable modulation frequency fm = Fref/Nss with Fref = Fin/N
0b000 => Nss = 512 (fm
≈
3.9 - 7.8 kHz)
0b001 => Nss
≈
384 (fm
≈
5.2 - 10.4 kHz)
0b010 => Nss = 256 (fm
≈
7.8 - 15.6 kHz)
0b011 => Nss = 128 (fm
≈
15.6 - 31.3 kHz)
0b100 => Nss = 64 (fm
≈
32.3 - 64.5 kHz)
0b101 => Nss = 32 (fm
≈
62.5- 125 kHz)
0b110 => Nss
≈
24 (fm
≈
83.3- 166.6 kHz)
0b111 => Nss = 16 (fm
≈
125- 250 kHz)
0
25:23
MR
Programmable frequency modulation depth
δ
fmodpk-pk = Fref x k/Fcco = k/MDdec
0 = no spread
0b000 => k = 0 (no spread spectrum)
0b001 => k
≈
1
0b010 => k
≈
1.5
0b011 => k
≈
2
0b100 => k
≈
3
0b101 => k
≈
4
0b110 => k
≈
6
0b111 => k
≈
8
0