UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
60 of 362
NXP Semiconductors
UM10208
Chapter 7: LPC2800 CGU
Table 44.
Initial Divider Control Register (HPNDEC - 0x8000 4CB4)
Bit
Symbol
Description
Reset
value
9:0
NDEC
If bit 4 of the HPMODE register is 0, the HS PLL first divides its input
clock by 1 through 256 inclusive. The value written to this register
depends on the divisor NSEL, and can be determined as described in
. The input clock and initial divisor must be selected so
that the result is between 4 kHz and 150 MHz. Lock indication is most
reliable if this result is between 100 kHz and 20 MHz.
0
31:10 -
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
-
Table 45.
Multiplier Control Register (HPMDEC - 0x8000 4CB0)
Bit
Symbol
Description
Reset
value
16:0
MDEC
The HS PLL multiplies the clock resulting from the initial division (if
any) by even values between 2 and 65536 inclusive. The value written
to this register depends on the multiplier MSEL, and can be
determined as described in
. The input clock, initial
divisor, and multiplier must be selected so that the multiplied clock is
between 275 and 550 MHz.
0
31:17 -
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
-
Table 46.
Final Divider Control Register (HPPDEC - 0x8000 4CB8)
Bit
Symbol
Description
Reset
value
6:0
PDEC
The output of the HS PLL is the multiplied clock divided by even values
between 2 and 64 inclusive. The value written to this register depends
on the divisor PSEL, and can be determined as described in
. Given the range limits on the multiplied clock, the HS
PLL can generate clocks between 4.3 and 275 MHz.
0
31:7
-
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
-
Table 47.
Mode Register (HPMODE - 0x8000 4CBC)
Bit
Symbol
Description
Reset
value
0
HPCLKEN A 1 in this bit enables the HP PLL output clock.
0
2
HPPD
A 1 in this bit powers down the HP PLL.
1
4
DIRECTI
A 1 in this bit disables the initial divider. Set this bit if it’s possible to
generate the desired output clock without the initial divider, as this
minimizes phase noise and jitter.
0
5
FREERUN A 1 in this bit disables feedback and allows the HP PLL to free run at
its current rate, even if the input clock is lost.
0
all
others
-
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
-