UM10375 All information provided in this document is subject to legal disclaimers. © 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 Figure 57
.
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
TICKINTCOUNTFLAG
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
[1]
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
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