CP3SP33SMSSLASHNOPB datasheet(315/407 Pages) TI1

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SLCLK

TIMER

(TWTM0 1) prescaler

CP3SP33

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SNOSCW5 – MAY 2013

31 Timing and Watchdog Module

The Timing and Watchdog Module (TWM) generates the clocks and interrupts used for timing periodic

functions in the system; it also provides Watchdog protection over soft- ware execution.

The TWM is designed to provide flexibility in system design by configuring various clock ratios and by

selecting the Watchdog clock source. After setting the TWM configuration, software can lock it for a higher

level of protection against erroneous software action. Once the TWM is locked, only reset can release it.

31.1 TWM Structure

Figure 115 is a block diagram showing the internal structure of the Timing and Watchdog module. There

are two main sections: the Real-Time Timer (T0) section at the top and the Watchdog section on the

bottom.

All counting activities of the module are based on the Slow Clock (SLCLK). A prescaler counter divides

this clock to make a slower clock. The prescaler factor is defined by a 3- bit field in the Timer and

Watchdog Prescaler register, which selects either 1, 2, 4, 8, 16, or 32 as the divisor. Therefore, the

prescaled clock period can be 2, 4, 8, 16, or 32 times the Slow Clock period. The prescaled clock signal is

called T0IN.

31.2 Timer to Operation

Timer T0 is a programmable 16-bit down counter that can be used as the time base for real-time

operations such as a periodic audible tick. It can also be used to drive the Watch- dog circuit.

The timer starts counting from the value loaded into the TWMT0 register and counts down on each rising

edge of T0IN. When the timer reaches zero, it is automatically reloaded from the TWMT0 register and

continues counting down from that value. Therefore, the frequency of the timer is:

(12)

When an external crystal oscillator is used as the SLCLK source or when the fast clock is divided

accordingly, fSLCLK is 32.768 kHz.

The value stored in TWMT0 can range from 0001h to FFFFh.

Timing and Watchdog Module

315

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CP3SP33SMS/NOPB Datasheet(PDF) 315 Page - Texas Instruments