41081 Chapter Notes - Chapter 4: Global Variable, Interrupt

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5 Jun 2018

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Chapter 4 – Time intervals

Time-Interval Behaviour

• Time-interval behaviour is system functionality where events must be separated by

specified intervals of real time.

• A tie iterval a e related to a eedded sste’s iput i additio to its

output.

Synchronous SMs

• The tick rate of an SM can be set to a specific time interval, known as the period.

• SMs with a specific period are known as synchronous SMs.

• In between ticks, the system is inactive. During this time, variables maintain their

values.

Choosing a Period for Different Time Intervals

• Choose the period as the greatest common divisor and then use multiple states to

obtain the actual desired interval. A count function can also be used where a

variable is incremented with each state transition.

Microcontrollers with Timers

• A timer is a hardware component that can be programmed to tick at a user-specified

rate.

• When the timer ticks, the hardware interrupts the program execution with an ISR

(Interrupt Service Routine) which will execute the TimerISR function before

resuming the main program.

• TimerSet(period) is used to set the timer duration in milliseconds, and TimerOn()

activates the timer.

• A flag is a global variable used by the program to communicate basic status info.

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