Page 159 - Digital Electronics by harish

Arithmetic or logic Arithmetic or logical

5. operation can be directly operation cannot be directly
performed with I/O data. performed with I/O data.

6. IO/ pin is not required. IO/ pin is required.

Instructions like LDA,
7. STA, MOV R,M and IN and OUT instructions are
used.
ADD M are used.

5.4.2 Interrupts

Interrupts are the signals send by an external device to the microprocessor
to request the microprocessor to perform a particular task or work. Interrupts are
used for data transfer between the peripheral and the microprocessor. The
microprocessor will check the interrupts always at the 2nd T-state of last
machine cycle. If there is any interrupt, it accepts the interrupt and sends the
signal to the peripheral. The microprocessor executes an interrupt service
routine (ISR) stored in memory. It returns to the main program by RET
instruction, after the ISR is executed. The interrupt process is shown in figure
5.15.

Figure 5.15 : Interrupt process

5.4.2.1 Types of interrupts

There are six types of interrupts. They are,
1. Hardware interrupts
2. Software interrupts
3. Maskable interrupts
4. Non-maskable interrupts
5. Vectored interrupts
6. Non-vectored interrupts

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