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Chapter 22
SWRU191C
–
April 2009
–
Revised January 2012
Timer 2 (MAC Timer)
Timer 2 is mainly used to provide timing for 802.15.4 CSMA-CA algorithms and for general timekeeping in
the 802.15.4 MAC layer on CC253x devices, for timekeeping in the BLE link layer on CC2540/41, and for
general radio timekeeping when running the radio in proprietary mode on CC2541. Timer 2 must not be
used by the application on the CC2540/41 when the BLE stack is running. When Timer 2 is used together
with the Sleep Timer, the timing function is provided even when the system enters low-power modes PM1
and PM2. The timer runs at a speed according to the system clock. If Timer 2 is to be used with the Sleep
Timer, the system clock source must be the 32-MHz crystal whenever Timer 2 is running, and an external
32-kHz XOSC should be used for accurate results.
The main features of Timer 2 are the following:
•
16-bit timer up-counter providing, for example, a symbol/frame period of 16
μ
s/320
μ
s
•
Adjustable period with accuracy of 31.25 ns
•
2
×
16-bit timer compare function
•
24-bit overflow count
•
2
×
24-bit overflow compare function
•
Start-of-frame-delimiter capture function
•
Timer start/stop synchronous with 32-kHz clock and timekeeping maintained by Sleep Timer.
•
Interrupts generated on compare and overflow
•
DMA trigger capability
•
Possible to adjust timer value while counting by introducing delay
Topic
...........................................................................................................................
Page
22.1
Timer Operation
..............................................................................................
22.2
Interrupts
........................................................................................................
22.3
Event Outputs (DMA Trigger and Radio Events)
..................................................
22.4
Timer Start/Stop Synchronization
......................................................................
22.5
Timer 2 Registers
............................................................................................
207
SWRU191C
–
April 2009
–
Revised January 2012
Timer 2 (MAC Timer)
Copyright
©
2009
–
2012, Texas Instruments Incorporated