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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
43 of 571
NXP Semiconductors
UM10316
Chapter 3: LPC29xx Clock Generation Unit (CGU)
5.11 Output-clock status register for CGU0 clocks
There is one status register for each CGU output clock generated. All output generators
have the same register bits. Exceptions are the output generators for BASE_SAFE_CLK
and BASE_PCR_CLK, see
5.12 Output-clock configuration register for CGU0 clocks
There is one configuration register for each CGU output clock generated. All output
generators have the same register bits. Exceptions are the output generators for
BASE_SAFE_CLK and BASE_PCR_CLK, see
.
XX = SYS, IVNSS, MSCSS, UART, SPI, TMR or ADC, ICLK0/1_CLK
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.
Table 24.
SAFE_CLK_CONF (address 0xFFFF 8068), PCR_CLK_CONF (address 0xFFFF
8078) register bit description
* = reset value
Bit
Symbol
Access
Value
Description
31 to 24 CLK_SEL
R/W
Selected source clock
00h*
LP_OSC
01h to
FFh
Invalid: the hardware will not accept these
values when written
23 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 to 0
reserved
R
-
Reserved; do not modify. Read as logic 0, write
as logic 0
Table 25.
XX_CLK_STATUS register bit description (XX = SYS (address 0xFFFF 806C),
IVNSS (address 0xFFFF 807C), MSCSS (address 0xFFFF 8084), UART (address
0xFFFF 8094), SPI (address 0xFFFF 809C), TMR (address 0xFFFF 80A4), ADC
(address 0xFFFF 80AC))
* = reset value
Bit
Symbol
Access
Value
Description
31 to 5
reserved
R
-
Reserved
4 to 2
IDIV
R
000*
Integer divide value
1
RTX
R
0*
Clock-disable polarity
0
PD
R
0*
Power-down clock slice