LM3S3749 Luminary Micro, Inc, LM3S3749 Datasheet - Page 47

• Manufacturer Part Number: LM3S3749
• Description: Lm3s3749 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

June 02, 2008
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.
Therefore, as a multi-shot timer, repeated over and over, it fires every N+1 clock pulse, where N is
any value from 1 to 0x00FF.FFFF. So, if the tick interrupt is required every 100 clock pulses, 99
must be written into the RELOAD. If a new value is written on each tick interrupt, so treated as single
shot, then the actual count down must be written. For example, if a tick is next required after 400
clock pulses, 400 must be written into the RELOAD.
SysTick Current Value Register
Use the SysTick Current Value Register to find the current value in the register.
SysTick Calibration Value Register
The SysTick Calibration Value register is not implemented.
Bit/Field
Bit/Field
Bit/Field
31:24
31:24
23:0
23:0
0
RELOAD
CURRENT
reserved
reserved
Name
Name
ENABLE
Name
Type
W1C
RO
Type
W1C
RO
Type
R/W
Reset
Reset
0
-
0
-
Reset
0
Description
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.
Reload
Value to load into the SysTick Current Value Register when the counter reaches 0.
Description
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.
Current Value
Current value at the time the register is accessed. No read-modify-write protection is
provided, so change with care.
This register is write-clear. Writing to it with any value clears the register to 0. Clearing
this register also clears the COUNTFLAG bit of the SysTick Control and Status Register.
Description
Enable
Value
0
1
Preliminary
Description
Counter disabled.
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.
LM3S3749 Microcontroller
47