UM10429
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User manual
Rev. 1 — 20 October 2010
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NXP Semiconductors
UM10429
Chapter 19: Appendix LPC1102 ARM Cortex-M0 reference
19.5.4.1 SysTick Control and Status Register
The SYST_CSR enables the SysTick features. See the register summary in for its
attributes. The bit assignments are:
19.5.4.2 SysTick Reload Value Register
The SYST_RVR specifies the start value to load into the SYST_CVR. See the register
summary in
for its attributes. The bit assignments are:
19.5.4.2.1
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.
19.5.4.3 SysTick Current Value Register
The SYST_CVR contains the current value of the SysTick counter. See the register
summary in
for its attributes. The bit assignments are:
Table 231. SYST_CSR bit assignments
Bits
Name
Function
[31:17]
-
Reserved.
[16]
COUNTFLAG
Returns 1 if timer counted to 0 since the last read of this register.
[15:3]
-
Reserved.
[2]
CLKSOURCE
Selects the SysTick timer clock source:
0 = external reference clock.
1 = processor clock.
Remark:
The external reference clock option is not implemented.
This bit reads as 1 and writes to this bit are ignored.
[1]
TICKINT
Enables SysTick exception request:
0 = counting down to zero does not assert the SysTick exception
request.
1 = counting down to zero asserts the SysTick exception request.
[0]
ENABLE
Enables the counter:
0 = counter disabled.
1 = counter enabled.
Table 232. 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