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
19.5.4.4 SysTick Calibration Value Register
The SYST_CALIB register indicates the SysTick calibration properties. See the register
summary in
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.
19.5.4.5 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.
19.6 Cortex-M0 instruction summary
Table 233. 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 234. 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.
Table 235. Cortex M0- instruction summary
Operation
Description
Assembler
Cycles
Move
8-bit immediate
MOVS Rd, #<imm>
1
Lo to Lo
MOVS Rd, Rm
1
Any to Any
MOV Rd, Rm
1
Any to PC
MOV PC, Rm
3
Add
3-bit immediate
ADDS Rd, Rn, #<imm>
1
All registers Lo
ADDS Rd, Rn, Rm
1
Any to Any
ADD Rd, Rd, Rm
1
Any to PC
ADD PC, PC, Rm
3