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UM10850
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© NXP B.V. 2016. All rights reserved.
User manual
Rev. 2.4 — 13 September 2016
49 of 464
NXP Semiconductors
UM10850
Chapter 4: LPC5410x System configuration (SYSCON)
4.5.37.2 System PLL status register
The read-only PLL0_STAT SYSPLLSTAT register provides the PLL lock status
Remark:
The lock status does not reliably indicate the PLL status for the following two
configurations: spread-spectrum mode or fractional enabled or low input clock frequencies
such as 32 kHz. In these cases, refer to the PLL lock times listed in the specific device
data sheet to obtain appropriate wait times for the PLL to lock.
4.5.37.3 System PLL N-divider register
Remark:
The PLL N-divider register does not use the direct binary representation of N
divide value directly. Instead, it uses an encoded version NDEC.
Remark:
While the PLL0 output is in use, do not change the NDEC value. Changing the
NDEC value changes the FCCO frequency and can cause the system to fail.
•
The valid range for N is 1 to 2^8. This value is encoded into a 10-bit NDEC value. The
relationship can be expressed through the following pseudo-code:
N_max=0x00000100, x=0x00000080;
switch (N) {
case 0: x = 0xFFFFFFFF;
case 1: x = 0x00000302;
case 2: x = 0x00000202;
default: for (i = N; i <= N_max; i++)
x = (((x ^ (x>>2) ^ (x>>3) ^ (x>>4)) & 1) << 7) |
((x>>1) & 0x7F); }
NENC[9:0] = x;
Table 67.
System PLL status register (SYSPLLSTAT, address 0x4000 01B4) bit description
Bit
Symbol
Description
Reset value
0
LOCK
PLL0 lock indicator
0
31:1
-
Reserved
-
Table 68.
System PLL N-divider register (SYSPLLNDEC, address 0x4000 01B8) bit description
Bit
Symbol
Description
Reset value
9:0
NDEC
Decoded N-divider coefficient value
0
10
NREQ
NDEC reload request. When a 1 is written to this bit, the NDEC value is loaded into the
PLL. Must be cleared by software for any subsequent load, or the PLL can be powered
down and back up via the PDEN_SYS_PLL bit in the PDRUNCFG register if the NDEC
value is changed.
0
31:11
-
Reserved. Read value is undefined, only zero should be written.
-