1206 Interrupts Of 8085
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1206 Interrupts Of 8085



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1206 Interrupts Of 8085 1206 Interrupts Of 8085 Presentation Transcript

  • Interrupts of 8085
  • Interrupt I/O
    • Memory-mapped & Peripheral-mapped I/O
      • process of data transfer b/w 8085 & I/O devices i nitiated by processor
    • Interrupt I/O
      • process of data transfer b/w 8085 & I/O devices initiated by an external device
      • allows an input/output device to inform the processor that it is ready for communication & requests attention.
  • 8085 Interrupts
    • 8085 has five interrupt inputs
    • TRAP
    • RST7.5
    • RST 6.5
    • RST5.5
    • INTR
  • Interrupt pins of 8085
  • Types of Interrupts
    • Interrupts of 8085 can be classified as
      • Maskable (RST 7.5, RST 6.5, RST 5.5, INTR)
      • Non-maskable (TRAP)
    • An interrupt is a request for attention/service
    • 8085 may choose to service/not-service a maskable interrupt
    • 8085 cannot ignore a service request from a non-maskable interrupt
  • Interrupt process
    • 8085 is executing its main program
    • an interrupt is generated by an external device
    • 8085 pauses execution of main program
    • 8085 calls the Interrupt service routine
    • 8085 executes the Interrupt service routine
    • 8085 returns to execution of main program (from where it was paused)
  • Example: Blinking LED Display with Interrupt-based Display-Pattern change 8085 Input Switches LED Display RST 7.5 (Display-Pattern ) Interrupt Switch Peripheral-mapped I/O Interrupt I/O
  • Interrupt Service Routine (ISR)
    • It is a subroutine
    • 8085 calls an ISR in response to an interrupt request by an external device
    • ISRs must be located in memory at pre-determined addresses known as Interrupt Vectors
  • Interrupt Vector Table of 8085 Please Note: INTR is a non-vectored interrupt 002CH RST 5.5 0034H RST 6.5 003CH RST 7.5 0024H TRAP Interrupt Vector Interrupt
  • Using Vectored Interrupts of 8085
    • By default, all the vectored interrupts (except TRAP) of 8085 are disabled
    • 8085 vectored interrupts are enabled with two instructions: EI and SIM
    • EI (Enable Interrupt) : 1-byte instruction that sets the Interrupt Enable flip-flop
      • It is internal to the processor & can be set or reset by using software instructions
  • Using Vectored Interrupts
    • Step-1
    • Set Interrupt Enable flip-flop by using EI instruction to enable the interrupt process
    • Step-2
    • Use SIM (Set Interrupt Mask) instruction to set mask for RST 7.5, 6.5 and 5.5 interrupts
  • SIM Instruction
    • It is a 1-byte instruction
    • Reads Accumulator contents
    • Enables/Disables interrupts accordingly
    • Used for three different functions
      • Set mask for RST 7.5, 6.5, 5.5 interrupts
      • Additional control for RST 7.5
      • Implement serial I/O
  • Accumulator bit pattern for SIM 0 = Available , 1 = Masked Mask Set Enable, 0 = bits 0-2 ignored 1 = mask is set IF 1, RESET RST 7.5 If 1, bit 7 is output to serial output data latch Serial Output Data, ignored if bit 6 = 0 M5.5 M6.5 M7.5 MSE R7.5 XXX SDE SOD D0 D1 D2 D3 D4 D5 D6 D7
  • 8085 Interrupt process for Vectored-Interrupts
    • Enables Interrupt process by writing the EI instruction in the main program
    • Set interrupt mask using SIM instruction
    • 8085 monitors the status of all interrupt lines during the execution of each instruction
    • When 8085 detects an interrupt signal from an external device
      • It completes execution of current instruction
      • Disables the Interrupt Enable flip-flop
    • Executes a CALL to Interrupt Vector location for that interrupt
      • Before the CALL is made, 8085 stores return address in main program on stack
    8085 Interrupt process for Vectored-Interrupts (Cont.)
    • 8085 executes the ISR written at the specified interrupt vector location
      • ISR should include the EI instruction to Enable Interrupt again
      • At the end of ISR, RET instruction transfers the program control back to the main program
    8085 Interrupt process for Vectored-Interrupts (Cont.)
  • Interrupt Programming
    • Problem statement:
    • Write a program for blinking a LED display (port address 80H) with interrupt-based display pattern change .
    • Write a subroutine to generate a delay of 50ms with 1MHz clock to set the blink rate.
    • Write a Interrupt Service Routine for vectored interrupt RST6.5 to read the display pattern for blinking from an input port with address 8000H