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UM10375
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 3 — 14 June 2011
296 of 368
NXP Semiconductors
UM10375
Chapter 17: LPC13xx System tick timer
17.6.1 System Timer Control and status register (CTRL - 0xE000 E010)
The CTRL register contains control information for the System Tick Timer, and provides a
status flag.
17.6.2 System Timer Reload value register (LOAD - 0xE000 E014)
The LOAD register is set to the value that will be loaded into the System Tick Timer
whenever it counts down to zero. This register is loaded by software as part of timer
initialization. The CALIB register may be read and used as the value for LOAD if the CPU
or external clock is running at the frequency intended for use with the CALIB value.
17.6.3 System Timer Current value register (VAL - 0xE000 E018)
The VAL register returns the current count from the System Tick counter when it is read by
software.
Table 285. System Timer Control and status register (CTRL - 0xE000 E010) bit description
Bit
Symbol
Description
Reset
value
0
ENABLE
System Tick counter enable. When 1, the counter is enabled.
When 0, the counter is disabled.
0
1
TICKINT
System Tick interrupt enable. When 1, the System Tick interrupt
is enabled. When 0, the System Tick interrupt is disabled. When
enabled, the interrupt is generated when the System Tick counter
counts down to 0.
0
2
CLKSOURCE System Tick clock source selection. When 1, the system clock
(CPU) clock is selected. When 0, the output clock from the
system tick clock divider (SYSTICKDIV) is selected as the
reference clock. In this case, the core clock must be at least 2.5
times faster than the reference clock otherwise the count values
are unpredictable.
0
15:3
-
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
NA
16
COUNTFLAG System Tick counter flag. This flag is set when the System Tick
counter counts down to 0, and is cleared by reading this register.
0
31:17 -
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
NA
Table 286. System Timer Reload value register (LOAD - 0xE000 E014) bit description
Bit
Symbol
Description
Reset
value
23:0
RELOAD
This is the value that is loaded into the System Tick counter when it
counts down to 0.
0
31:24
-
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
NA