UM10346_1
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 01 — 2 November 2009
41 of 132
NXP Semiconductors
UM10346
LPC980/982 User manual
•
Brownout detect;
•
Watchdog timer;
•
Software reset;
•
UART break character detect reset.
For every reset source, there is a flag in the Reset Register, RSTSRC. The user can read
this register to determine the most recent reset source. These flag bits can be cleared in
software by writing a ‘0’ to the corresponding bit. More than one flag bit may be set:
•
During a power-on reset, both POF and BOF are set but the other flag bits are
cleared.
•
A watchdog reset is similar to a power-on reset, both POF and BOF are set but the
other flag bits are cleared.
•
For any other reset, previously set flag bits that have not been cleared will remain set.
[1]
The value shown is for a power-on reset. Other reset sources will set their corresponding bits.
Fig 13. Block diagram of reset
RPE (UCFG1.6)
RST pin
WDTE (UCFG2.7)
watchdog timer reset
software reset SRST (AUXR1.3)
power-on detect
UART break detect
EBRR (AUXR1.6)
brownout detect reset
chip reset
002aae587
Table 28.
Reset Sources register (RSTSRC - address DFh) bit allocation
Bit
7
6
5
4
3
2
1
0
Symbol
-
BOIF
BOF
POF
R_BK
R_WD
R_SF
R_EX
Reset
x
0
1
1
0
0
0
0
Table 29.
Reset Sources register (RSTSRC - address DFh) bit description
Bit Symbol Description
0
R_EX
external reset Flag. When this bit is logic 1, it indicates external pin reset. Cleared by software by writing a
logic 0 to the bit or a Power-on reset. If RST is still asserted after the Power-on reset is over, R_EX will be set.
1
R_SF
software reset Flag. Cleared by software by writing a logic 0 to the bit or a Power-on reset
2
R_WD
Watchdog Timer reset flag. Cleared by software by writing a logic 0 to the bit or a Power-on reset.(NOTE:
UCFG2.7 must be = 1)
3
R_BK
break detect reset. If a break detect occurs and EBRR (AUXR1.6) is set to logic 1, a system reset will occur.
This bit is set to indicate that the system reset is caused by a break detect. Cleared by software by writing a
logic 0 to the bit or on a Power-on reset.