DR
AFT
DR
AFT
DRAFT
DR
D
RAFT
DRAFT
DRA
FT DRAF
D
RAFT DRAFT DRAFT DRAFT DRAFT D
DRAFT
D
RAFT DRA
FT DRAFT DRAFT DRAFT DRA
UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
35 of 571
NXP Semiconductors
UM10316
Chapter 3: LPC29xx Clock Generation Unit (CGU)
value. Secondly, due to synchronization, the counters are not started and stopped at
exactly the same time. Finally, the measured frequency can only be to the same level of
precision as the reference frequency.
Remark:
The clock selection in this register depends on whether the register is used for
CGU0 or CGU1. In the CGU0, the low-power oscillator (LP_OSC) or the external crystal
oscillator can be selected as input. In the CGU1, the two CGU0 base clocks
BASE_ICLK0_CLK and BASE_ICLK1_CLK, can be selected instead. CGU1 has only one
fractional divider register.
5.2 Clock detection register
Each clock generator has a clock detector associated with it to alert the system if a clock
is removed or connected. The status register RDET can determine the current
‘clock-present’ status.
If enabled, interrupts are generated whenever ‘clock present’ changes status, so that an
interrupt is generated if a clock changes from ‘present’ to ‘non-present’ or from
‘non-present’ to ‘present’.
Table 15.
FREQ_MON register bit description (FREQ_MON, address 0xFFFF 8014 (CGU0)
and 0xFFFF B014 (CGU1))
* = reset value
Bit
Symbol
Access
Value
Description
31 to 24 CLK_SEL
R/W
Clock-source selection for the clock to be
measured.
00h*
LP_OSC (CGU0) or BASE_ICLK0_CLK
(CGU1)
01h
Crystal oscillator (CGU0) or BASE_ICLK1_CLK
(CGU1)
02h
PLL
03h
PLL +120
°
04h
PLL +240
°
05h
FDIV0 (CGU0 and CGU1)
06h
FDIV1 (CGU0 only)
07h
FDIV2 (CGU0 only)
08h
FDIV3 (CGU0 only)
09h
FDIV4 (CGU0 only)
0Ah
FDIV5 (CGU0 only)
0Bh
FDIV6 (CGU0 only)
23
MEAS
R/W
Measure frequency
0*
22 to 9
FCNT
R
Selected clock-counter value
000h*
8 to 0
RCNT
R/W
Reference clock-counter value
000h*