LM3S6952 Datasheet, PDF (50/626 Pages) Texas Instruments – Stellaris LM3S6952 Microcontroller

ARM Cortex-M3 Processor Core
If the core is in debug state (halted), the counter will not decrement. The timer is clocked with respect
to a reference clock. The reference clock can be the core clock or an external clock source.
SysTick Control and Status Register
Use the SysTick Control and Status Register to enable the SysTick features. The reset is
0x0000.0000.
Bit/Field
31:17
Name
reserved
16 COUNTFLAG
15:3
reserved
2 CLKSOURCE
Type
RO
R/W
RO
R/W
Reset Description
0 Software should not rely on the value of a reserved bit. To provide compatibility
with future products, the value of a reserved bit should be preserved across
a read-modify-write operation.
0 Count Flag
Returns 1 if timer counted to 0 since last time this was read. Clears on read
by application. If read by the debugger using the DAP, this bit is cleared on
read-only if the MasterType bit in the AHB-AP Control Register is set to 0.
Otherwise, the COUNTFLAG bit is not changed by the debugger read.
0 Software should not rely on the value of a reserved bit. To provide compatibility
with future products, the value of a reserved bit should be preserved across
a read-modify-write operation.
0 Clock Source
Value Description
0 External reference clock. (Not implemented for Stellaris
microcontrollers.)
1 Core clock
If no reference clock is provided, it is held at 1 and so gives the same time as
the core clock. The core clock must be at least 2.5 times faster than the
reference clock. If it is not, the count values are unpredictable.
1
TICKINT
R/W
0 Tick Interrupt
Value Description
0 Counting down to 0 does not generate the interrupt request to the
NVIC. Software can use the COUNTFLAG to determine if ever counted
to 0.
1 Counting down to 0 pends the SysTick handler.
0
ENABLE
R/W
0 Enable
Value Description
0 Counter disabled.
1 Counter operates in a multi-shot way. That is, counter loads with the
Reload value and then begins counting down. On reaching 0, it sets
the COUNTFLAG to 1 and optionally pends the SysTick handler, based
on TICKINT. It then loads the Reload value again, and begins counting.
SysTick Reload Value Register
Use the SysTick Reload Value Register to specify the start value to load into the current value
register when the counter reaches 0. It can be any value between 1 and 0x00FF.FFFF. A start value
of 0 is possible, but has no effect because the SysTick interrupt and COUNTFLAG are activated
when counting from 1 to 0.
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April 05, 2010
Texas Instruments-Production Data