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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
479 of 808
NXP Semiconductors
UM10360
Chapter 23: LPC17xx System Tick Timer
5.2 System Timer Reload value register (STRELOAD - 0xE000 E014)
The STRELOAD 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 STCALIB register may be read and used as the value for STRELOAD if
the CPU or external clock is running at the frequency intended for use with the STCALIB
value.
5.3 System Timer Current value register (STCURR - 0xE000 E018)
The STCURR register returns the current count from the System Tick counter when it is
read by software.
5.4 System Timer Calibration value register (STCALIB - 0xE000 E01C)
The STCALIB register contains a value that is initialized by the Boot Code to a factory
programmed value that is appropriate for generating an interrupt every 10 milliseconds if
the System Tick Timer is clocked at a frequency of 100 MHz. This is the intended use of
the System Tick Timer by ARM. It can be used to generate interrupts at other frequencies
by selecting the correct reload value.
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 420. System Timer Control and status register (STCTRL - 0xE000 E010) bit description
Bit
Symbol
Description
Reset value
Table 421. System Timer Reload value register (STRELOAD - 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
Table 422. System Timer Current value register (STCURR - 0xE000 E018) bit description
Bit
Symbol
Description
Reset value
23:0
CURRENT
Reading this register returns the current value of the System Tick
counter. Writing any value clears the System Tick counter and the
COUNTFLAG bit in STCTRL.
0
31:24
-
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA