CC2430-RTR1-F32 datasheet(110/234 Pages) TI

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CC2430

CC2430 PRELIMINARY Data Sheet (rev. 1.03) SWRS036A

Page 110 of 232

13.4 MAC Timer (Timer 2)

The MAC Timer is mainly used to provide

timing for 802.15.4 CSMA-CA algorithms

and for general timekeeping in the

802.15.4 MAC layer. When the MAC

Timer is used together with the Sleep

Timer described in section 13.5, the timing

function is provided even when the system

enters low-power modes.

The main features of the MAC Timer are

the following:

•

16-bit timer up-counter providing

symbol/frame period: 16µs/320µs

•

Adjustable period with accuracy

31.25 ns

•

8-bit timer compare function

•

20-bit overflow count

•

20-bit overflow count compare

function

•

Start of Frame Delimiter capture

function.

•

Timer start/stop synchronous with

32.768 kHz clock and timekeeping

maintained by Sleep Timer.

•

Interrupts generated on compare

and overflow

•

DMA trigger capability

13.4.1 Timer Operation

This section describes the operation of the

timer.

13.4.1.1 General

After a reset the timer is in the timer IDLE

mode where it is stopped. The timer starts

running when T2CNF.RUN is set to 1. The

timer will then enter the timer RUN mode.

The entry is either immediate or it is

performed synchronous with the 32.768

kHz clock. See section 13.4.4 for a

description of the synchronous start and

stop mode.

Once the timer is running in RUN mode, it

can be stopped by writing a 0 to

T2CNF.RUN. The timer will then enter the

timer IDLE mode. The stopping of the

timer is performed either immediately or it

is performed synchronous with the 32.768

kHz clock

13.4.1.2 Up Counter

The MAC Timer contains a 16-bit timer,

which increments during each clock cycle.

13.4.1.3 Timer overflow

When the timer is about to count to a

value that is equal to or greater than the

timer

period

set

registers

T2CAPHPH:T2CAPLPL, a timer overflow

occurs. When the timer overflow occurs,

the timer value is set to the difference

between the value it is about to count to

and the timer period during the next clock

cycle. If the overflow interrupt mask bit

T2PEROF2.PERIM is 1, an interrupt

request is generated. The interrupt flag bit

T2CNF.PERIF is set to 1 regardless of the

interrupt mask value.

13.4.1.4 Timer delta increment

The timer period may be adjusted once

during a timer period by writing a timer

delta value. When a timer delta value is

written to the registers T2THD:T2TLD, the

16-bit timer halts at its current value and a

delta counter starts counting. The delta

counter starts counting from the delta

value written, down to zero. Once the delta

counter reaches zero, the 16-bit timer

starts counting again.

The delta counter decrements by the

same rate as the timer. When the delta

counter has reached zero it will not start

counting again until the delta value is

written once again. In this way a timer

period may be increased by the delta

value in order to make adjustments to the

timer overflow events over time.

13.4.1.5 Timer Compare

A timer compare occurs when the timer is

about to count to a value that is equal or

greater than the 8-bit compare value held

in the T2CMP register. Note that the

compare value is only 8 bits so the

compare is made between the compare

value and either the most significant byte

or the least significant byte of the timer.

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