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UM10375
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 3 — 14 June 2011
295 of 368
NXP Semiconductors
UM10375
Chapter 17: LPC13xx System tick timer
17.5 Operation
The System Tick 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 System Tick Timer is clocked from the CPU clock. In order to generate recurring
interrupts at a specific interval, the LOAD register must be initialized with the correct value
for the desired interval.
The block diagram of the System Tick Timer is shown below in the
.
17.6 Register description
[1]
Reset Value reflects the data stored in used bits only. It does not include content of reserved bits.
Fig 57. System tick timer block diagram
STCALIB
STRELOAD
STCURR
24-bit down counter
ENABLE
STCTRL
private
peripheral
bus
System Tick
interrupt
TICKINT
COUNTFLAG
load
under-
flow
count
enable
clock
load data
CLKSOURCE
system clock
Systick clock
Table 284. Register overview: system tick timer (base address 0xE000 E000)
Name
Access
Address
offset
Description
Reset value
CTRL
R/W
0x010
System Timer Control and status register
0x0
LOAD
R/W
0x014
System Timer Reload value register
0x0
VAL
R/W
0x018
System Timer Current value register
0x0
CALIB
RO
0x01C
System Timer Calibration value register
0x0000 0004