Datasheet

UM10398 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
User manual Rev. 12.3 — 10 June 2014 406 of 547
NXP Semiconductors
UM10398
Chapter 24: LPC111x/LPC11Cxx System tick timer (SysTick)
24.5.2 System Timer Reload value register
The SYST_RVR register is set to the value that will be loaded into the SysTick timer
whenever it counts down to zero. This register is loaded by software as part of timer
initialization. The SYST_CALIB register may be read and used as the value for
SYST_RVR register if the CPU is running at the frequency intended for use with the
SYST_CALIB value.
24.5.3 System Timer Current value register
The SYST_CVR register returns the current count from the System Tick counter when it is
read by software.
Table 358. SysTick Timer Control and status register (SYST_CSR - 0xE000 E010) bit
description
Bit Symbol Description Reset
value
0 ENABLE System Tick counter enable. When 1, the counter is enabled.
When 0, the counter is disabled.
0
1 TICKINT System Tick interrupt enable. When 1, the System Tick interrupt
is enabled. When 0, the System Tick interrupt is disabled. When
enabled, the interrupt is generated when the System Tick counter
counts down to 0.
0
2 CLKSOURCE System Tick clock source selection. When 1, the system clock
(CPU) clock is selected. When 0, the system clock/2 is selected
as the reference clock.
0
15:3 - Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
NA
16 COUNTFLAG Returns 1 if the SysTick timer counted to 0 since the last read of
this register.
0
31:17 - Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
NA
Table 359. System Timer Reload value register (SYST_RVR - 0xE000 E014) bit description
Bit Symbol Description Reset
value
23:0 RELOAD This is the value that is loaded into the System Tick counter when it
counts down to 0.
0
31:24 - Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
NA
Table 360. System Timer Current value register (SYST_CVR - 0xE000 E018) bit description
Bit Symbol Description Reset
value
23:0 CURRENT Reading this register returns the current value of the System Tick
counter. Writing any value clears the System Tick counter and the
COUNTFLAG bit in STCTRL.
0
31:24 - Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA