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DRAFT
DR
D
RAFT
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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
45 of 571
NXP Semiconductors
UM10316
Chapter 3: LPC29xx Clock Generation Unit (CGU)
5.14 Output-clock configuration register for CGU1 clocks
There is one configuration register for each CGU1 output clock generated. All output
generators have the same register bits. The CGU1 output clock can be generated directly
from the two CGU0 base clocks BASE_ICLK0_CLK and BASE_ICLK1_CLK or from the
CGU1 PLL.
Each output generator takes in one input clock and sends one clock out of the CGU. In
between the clock passes through an integer divider and a clock control block. A clock
blocker/switch block connects to the clock control block.
The integer divider has a 3-bit control signal, IDIV, and divides the incoming clock by any
value from 1 through 8. The divider value is equal to (IDIV + 1); if IDIV is equal to zero, the
incoming clock is passed on directly to the next stage. When the input to the integer
divider has a 50% duty cycle the divided output will have a 50% duty cycle for all divide
values. If the incoming duty cycle is not 50% only even divide values will produce an
output clock with a 50% duty cycle.
[1]
When JTAG = 1, crystal Oscillator will be the default value for the BASE_SYS_CLK
5.15 Bus disable register
The BUS_DISABLE register prevents any disabled register in the CGU0 from being
written to.
Table 28.
XX_CLK_CONF register bit description (XX = USB_CLK (address 0xFFFF B030),
USB_I2C_CLK (address 0xFFFF B038), OUT_CLK (address 0xFFFF B040))
* = reset value
Bit
Symbol
Access
Value
Description
31 to 24 CLK_SEL
R/W
selected source clock
00h*
BASE_ICLK0_CLK
01h
BASE_ICLK1_CLK
02h
PLL
03h
PLL +120
0
04h
PLL +240
0
05h
FDIV0
06h -
0Bh
reserved
23 to 12 reserved
R
-
Reserved
11
AUTOBLOK
W
-
Enables auto-blocking of clock when
programming changes
10 to 5
reserved
R
-
Reserved; do not modify. Read as logic 0, write
as logic 0
4 to 2
IDIV
R/W
000*
Integer divide value
1
reserved
R/W
0*
Reserved; do not modify. Read as logic 0, write
as logic 0
0
PD
R/W
0*
Power-down clock slice