UM10562 Datasheet, PDF (701/942 Pages) NXP Semiconductors – LPC408x/407x User manual

NXP Semiconductors
UM10562
Chapter 25: LPC408x/407x System Tick timer
25.5.3 System Timer Current value register
The STCURR register returns the current count from the System Tick counter when it is
read by software.
Table 550. System Timer Current value register (STCURR - 0xE000 E018) bit description
Bit Symbol Description
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.
31:24 -
Reserved. Read value is undefined, only zero should be written.
Reset value
0
NA
25.5.4 System Timer Calibration value register
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.
Table 551. System Timer Calibration value register (STCALIB - 0xE000 E01C) bit description
Bit Symbol Description
Reset value
23:0 TENMS
Reload value to get a 10 millisecond System Tick underflow rate when running at 100
MHz. This value initialized at reset with a factory supplied value selected for the
LPC408x/407x. The provided values of TENMS, SKEW, and NOREF are applicable only
when using a CPU clock or external STCLK source of 100 MHz.
0x0F 423F
29:24 -
Reserved. Read value is undefined, only zero should be written.
NA
30 SKEW Indicates whether the TENMS value will generate a precise 10 millisecond time, or an
0
approximation. This bit is initialized at reset with a factory supplied value selected for the
LPC408x/407x. See the description of TENMS above.
When 0, the value of TENMS is considered to be precise. When 1, the value of TENMS is
not considered to be precise.
31 NOREF Indicates whether an external reference clock is available. This bit is initialized at reset
0
with a factory supplied value selected for the LPC408x/407x. See the description of
TENMS above.
When 0, a separate reference clock is available. When 1, a separate reference clock is
not available.
UM10562
User manual
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Rev. 1 — 13 September 2012
© NXP B.V. 2012. All rights reserved.
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