PERIODIC INTERRUPTS, WAVEFORM GENERATION, TIME MEASUREMENT Flashcards
A signal to the processor emitted by hardware or software indicating an event that needs immediate attention.
INTERRUPTS
INTERRUPTS
* ______ programming concept
* E_I_
* I
- Low level
- Extremely important
- Irreplaceable
ORIGIN OF INTERRUPTS
* Normal view of a computer program: sequence of instructions executed _____ , jumps are allowed
serially
ORIGIN OF INTERRUPTS
* This view ______ for the real world.
isn’t good enough
ORIGIN OF INTERRUPTS
* Programs for embedded systems usually service
_______
real-life demands
ORIGIN OF INTERRUPTS
* Real-life demands _____ for anything.
don’t wait
ORIGIN OF INTERRUPTS
* Consider a typical embedded system program: it usually consists of an infinite loop, called the _________
“program loop”
ORIGIN OF INTERRUPTS
* In each iteration, the program checks whether
_________ (i), gives _______ (ii) and
performs ___________ (iii).
i. events have occurred
ii. suitable responses
iii. periodic tasks
ORIGIN OF INTERRUPTS
* This model is sufficient if processor is __________ with respect to real world
extremely fast
Why Interrupts?
* We need a method to ______ the moment they occur, and not after some delayed time.
handle events
Why Interrupts?
* ______ are special events that can “interrupt” the normal flow of a program.
Interrupts
Why Interrupts?
* The ______ stops the normal program, handles the interrupt, and then resumes its normal work.
processor
An electronic alerting signal sent from the processor from an external device, like a disk controller or an external peripheral
Hardware Interrupts
Caused either by an exceptional condition or a special instruction in the instruction set which causes an interrupt when it is executed by the processor.
Software Interrupts
- The state of continuous monitoring
- The microcontroller keeps checking the status of other devices
Polling
For every interrupt, there must be an ________,
or interrupt handler. When an interrupt occurs, the microcontroller runs the __________
interrupt service routine (ISR)
The table of memory locations set aside to hold the addresses of ISRs is called as the ______
Interrupt Vector Table
Two types of Interrupt modules
- LEVEL TRIGGERED
- EDGE TRIGGERED
Enabling and Disabling an Interrupt
* Upon _____, all the interrupts are disabled even if they are activated. The interrupts must be enabled using software in order for the microcontroller to respond to those interrupts.
Reset
Enabling and Disabling an Interrupt
* ______ is responsible for enabling and disabling the interrupt.
* _______ is a bitaddressable register.
IE (interrupt enable) register
Types of Interrupt Enable Register
- EA
- -
- ET2
- ES
- ET1
- EX1
- ET0
- EX0
Interrupt Enable Register
* Global enable/disable
EA
Interrupt Enable Register
* Undefined
-
Interrupt Enable Register
* Enable Timer 2 interrupt
ET2
Interrupt Enable Register
* Enable Serial port interrupt.
ES
Interrupt Enable Register
* Enable Timer 1 interrupt.
ET1
Interrupt Enable Register
* Enable External 1 interrupt
EX1
Interrupt Enable Register
*Enable Timer 0 interrupt.
ET0
Interrupt Enable Register
* Enable External 0 interrupt.
EX0
What happens if the 8051 is executing an ISR that
belongs to an interrupt and another one gets
active?
In such cases, a high-priority interrupt can interrupt a low-priority interrupt. This is known as interrupt inside interrupt. In 8051, a low-priority interrupt can be interrupted by a high-priority interrupt, but not by any another low-priority interrupt
______ is a register. Recall that registers are special, fixed-size variables with hardware implications
Timer
The timer, when started,
begins at __ (i) . After every time t, its value increases by ___ (ii).
i. 0
ii. 1
When the timer reaches its maximum value, in the next cycle, its value becomes __ again and the process repeats itself
0
TIMERS CAN GENERATE CERTAIN INTERRUPTS:
Two
is generated when a timer tries to exceed its maximum value and resets to 0.
OVERFLOW
There is a register called as _________, whose value we can set
OCR (Output Compare Register)
A timer works in
three modes:
Normal, CTC and
PWM.
Timer starts at 0, goes to
maximum value and
then resets itself.
Standard mode
Timer starts at 0 as usual, but instead of resetting
after maximum value, it resets after reaching
value specified in OCR register
CTC (Clear Timer on Compare) Mode
- Simple method of obtaining analog output of any value between 0 and 5V.
- This “analog” value is obtained using timers.
PWM (Phase Width Modulation) Mode
