User Manual

UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2010. All rights reserved.
User manual Rev. 2 — 19 August 2010 506 of 840
NXP Semiconductors
UM10360
Chapter 23: LPC17xx System Tick Timer
23.5.2 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.
23.5.3 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.
23.5.4 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 439. System Timer Control and status register (STCTRL - 0xE000 E010) bit description
Bit Symbol Description Reset value
Table 440. 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 441. 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