UM10429
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User manual
Rev. 1 — 20 October 2010
137 of 258
NXP Semiconductors
UM10429
Chapter 15: LPC1102 System tick timer
15.5 Operation
The SysTick timer is a 24-bit timer that counts down to zero and generates an interrupt.
The intent is to provide a fixed 10 millisecond time interval between interrupts. The
SysTick timer is clocked from the CPU clock. In order to generate recurring interrupts at a
specific interval, the SYST_RVR register must be initialized with the correct value for the
desired interval. A default value (<tbd>) is provided in the SYST_CALIB register and may
be changed by software. The default value gives a 10 millisecond interrupt rate if the CPU
clock is set to <tbd>.
The block diagram of the SysTick timer is shown below in the
.
15.6 Register description
The systick timer registers are located on the ARM Cortex-M0 private peripheral bus (see
), and are part of the ARM Cortex-M0 core peripherals. For details, see
[1]
Reset Value reflects the data stored in used bits only. It does not include content of reserved bits.
Fig 30. System tick timer block diagram
system clock/2
SYST_CALIB
SYST_RVR
SYST_CVR
24-bit down counter
ENABLE
SYST_CSR
private
peripheral
bus
System Tick
interrupt
TICKINT
COUNTFLAG
load
under-
flow
count
enable
clock
load data
Table 135. Register overview: SysTick timer (base address 0xE000 E000)
Name
Access
Address
offset
Description
Reset value
SYST_CSR
R/W
0x010
System Timer Control and status register
0x000 0000
SYST_RVR
R/W
0x014
System Timer Reload value register
0
SYST_CVR
R/W
0x018
System Timer Current value register
0
SYST_CAL
R/W
0x01C
System Timer Calibration value register
0x4