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UM10375
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 3 — 14 June 2011
22 of 368
NXP Semiconductors
UM10375
Chapter 3: LPC13xx System configuration
3.5.10 System reset status register
The SYSRSTSTAT register shows the source of the latest reset event. The bits are
cleared by writing a one to any of the bits. The POR event clears all other bits in this
register, but if another reset signal (e.g., EXTRST) remains asserted after the POR signal
is negated, then its bit is set to detected.
3.5.11 System PLL clock source select register
This register selects the clock source for the system PLL. The SYSPLLCLKUEN register
(see
) must be toggled from LOW to HIGH for the update to take effect.
Remark:
The system oscillator must be selected if the system PLL is used to generate a
48 MHz clock to the USB block.
Remark:
When switching clock sources, both clocks must be running before the clock
source is updated.
Table 17.
System reset status register (SYSRESSTAT, address 0x4004 8030) bit description
Bit
Symbol
Value
Description
Reset
value
0
POR
POR reset status
0x0
0
No POR detected
1
POR detected
1
EXTRST
0x0
0
No RESET event detected
1
RESET detected
2
WDT
Status of the Watchdog reset
0x0
0
No WDT reset detected
1
WDT reset detected
3
BOD
Status of the Brown-out detect reset
0x0
0
No BOD reset detected
1
BOD reset detected
4
SYSRST
Status of the software system reset. The ARM software
reset has the same effect as the hardware reset using the
RESET pin.
0x0
0
No System reset detected
1
System reset detected
31:5
-
-
Reserved
0x00