UM10462 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2016. All rights reserved.
User manual Rev. 5.5 — 21 December 2016 497 of 523
NXP Semiconductors
UM10462
Chapter 24: LPC11U3x/2x/1x Appendix ARM Cortex-M0
24.5.4.2 SysTick Reload Value Register
The SYST_RVR specifies the start value to load into the SYST_CVR. See the register
summary in Table 24–451
for its attributes. The bit assignments are:
24.5.4.2.1 Calculating the RELOAD value
The RELOAD value can be any value in the range
0x00000001
-
0x00FFFFFF
. You can program a
value of 0, but this has no effect because the SysTick exception request and
COUNTFLAG are activated when counting from 1 to 0.
To generate a multi-shot timer with a period of N processor clock cycles, use a RELOAD
value of N-1. For example, if the SysTick interrupt is required every 100 clock pulses, set
RELOAD to 99.
24.5.4.3 SysTick Current Value Register
The SYST_CVR contains the current value of the SysTick counter. See the register
summary in Table 24–451
for its attributes. The bit assignments are:
24.5.4.4 SysTick Calibration Value Register
The SYST_CALIB register indicates the SysTick calibration properties. See the register
summary in Table 24–451
for its attributes. The bit assignments are:
[2] CLKSOURCE Selects the SysTick timer clock source:
0 = external reference clock
1 = processor clock.
[1] TICKINT Enables SysTick exception request:
0 = counting down to zero does not assert the SysTick exception
request
1 = counting down to zero to asserts the SysTick exception request.
[0] ENABLE Enables the counter:
0 = counter disabled
1 = counter enabled.
Table 452. SYST_CSR bit assignments
Bits Name Function
Table 453. SYST_RVR bit assignments
Bits Name Function
[31:24] - Reserved.
[23:0] RELOAD Value to load into the SYST_CVR when the counter is enabled and
when it reaches 0, see Section 24.5.4.2.1
.
Table 454. 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.
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