Datasheet

UM10398 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
User manual Rev. 12.3 — 10 June 2014 518 of 547
NXP Semiconductors
UM10398
Chapter 28: LPC111x/LPC11Cxx Appendix: ARM Cortex-M0 reference
28.6.4.4 SysTick Calibration Value Register
The SYST_CALIB register indicates the SysTick calibration properties. See the register
summary in Table 28–458
for its attributes. The bit assignments are:
If calibration information is not known, calculate the calibration value required from the
frequency of the processor clock or external clock.
28.6.4.5 SysTick usage hints and tips
The interrupt controller clock updates the SysTick counter. If this clock signal is stopped
for low power mode, the SysTick counter stops.
Ensure software uses word accesses to access the SysTick registers.
If the SysTick counter reload and current value are undefined at reset, the correct
initialization sequence for the SysTick counter is:
1. Program reload value.
2. Clear current value.
3. Program Control and Status register.
Table 461. SYST_CVR bit assignments
Bits Name Function
[31:24] - Reserved.
[23:0] CURRENT Reads return the current value of the SysTick counter.
A write of any value clears the field to 0, and also clears the
SYST_CSR.COUNTFLAG bit to 0.
Table 462. SYST_CALIB register bit assignments
Bits Name Function
[31] NOREF Reads as one. Indicates that no separate reference clock is provided.
[30] SKEW Reads as one. Calibration value for the 10ms inexact timing is not known
because TENMS is not known. This can affect the suitability of SysTick
as a software real time clock.
[29:24] - Reserved.
[23:0] TENMS Reads as zero. Indicates calibration value is not known.