Transcript
What is an Interrupt?
It means interrupting the normal execution of the microprocessor.
Steps whenever there is an interrupt?
current
PC PC contents are stored in stack
100
101
102
103
104
103
103
STACK
SP
4
Interrupts in 8085
Main routine
Interrupt
Save program counter
Disable interrupts
Send out interupt acknowledge
Service routine
INTA
Go to service routine
Get original program counter
Go back
EI
RET
HARDWARE INTERRUPT
It is a special signal from an I/O device to the computer.
SOFTWARE INTERRUPT
It is generated by a program interrupt instructions in the CPU.
TYPES OF INTERRUPTS
MASKABLE & NON- MASKABLE INTERRUPTS
VECTORED & NON-VECTORED INTERRUPTS
EDGE TRIGGERED & LEVEL TRIGGERED INTERRUPTS
PRIORITY BASED INTERRUPTS
MASKABLE INTERRUPTS
EXAMPLE: RST 7.5 RST 6.5 RST 5.5 INTR ONLY TRAP IS A NON MASKABLE
INTERRUPT
VECTORED INTERRUPTS
EXAMPLE:
RST 7.5 RST 6.5 RST 5.5 TRAP
8085 Interrupts
8085
TRAPRST7.5RST6.5RST 5.5INTRINTA
The addresses to which program control goes:
NAME VECTOR ADDRESSES
RST 7.5 003CH(7.5 X 0008H)
RST 6.5 0034H(6.5 X 0008H)
RST 5.5 002CH(5.5 X 0008H)
TRAP 0024H(4.5 X 0008H)
Absolute address is calculated by multiplying the RST value with 0008H.
NON – VECTORED INTERRUPT
EXAMPLE:
INTR is a non vectored interrupt.
The 8085 Interrupts
Interrupt name Maskable Vectored
INTR Yes No
RST 5.5 Yes Yes
RST 6.5 Yes Yes
RST 7.5 Yes Yes
TRAP No Yes
EDGE TRIGGERED INTERRUPTS
EXAMPLE:
RST 7.5
Edge triggering
Rising edge
Falling edge
LEVEL TRIGGERED INTERRUPT
EXAMPLE: RST 6.5 RST 5.5 INTR TRAP is EDGE & LEVEL triggered interrupt.
Level triggering
Low level
High level
PRIORITY BASED INTERRUPTSINTERRUPT PRIORITY
TRAP 1
RST 7.5 2
RST 6.5 3
RST 5.5 4
INTR 5
Five hardware interrupts are:
TRAP RST 7.5 RST 6.5 RST 5.5 INTR
TRAP (PIN-6)
Non- maskable Has highest priority Can not disable. Edge & level triggered Used for power failure & emergency shut off.
RST 7.5
Maskable interrupt.
Has 2nd highest priority.
+ve edge triggered only.
RST 6.5
Maskable interrupt.
3rd highest priority.
Level triggered only.
RST 5.5
Maskable interrupt.
4th highest priority.
Level triggered only.
INTR
Maskable interrupt.
Lowest priority.
Level triggered.
INTA’
Stands for Interrupt acknowledge.
Outgoing signal.
Active low signal.
QUESTIONS FOR YOU
Which interrupt has the highest priority?
Which interrupt has the lowest priority?
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