ECE 38 - quiz 3

• 8085 uP Architecture - essential componets:

  accumulator

  general purpose registers

  program status write

  program counter
• accumulator (A)


  used to store 8-bit data and to perform arithmetic and logical operations

  the result of the operation is stored in this
• general purpose register

  
  

  • 8085 uP has 6 gpr each of which has 8-bits
  • the registers can be used for data manipulation and storage
• program status write

  • in flag registers, five bits (D7, D6, D4, D2, D0) indicate 5 status flags
  • the three bits (D5, D3, D1) are undefined
• program counter

  • 16-bit register that holds the memory address of the memory address of the next following instruction for fetching and executing
  • it automatically increments after each instruction fetch allowing programs to execute the next instruction quickly.
• adress and data buses:

  • the 8085 uP has 16-bit address bus allowing it to adress up to 64KB of memory
  • it also has an 8-bit data bus for transferring between the uP and memory or I/O devices
• interrupt control group

  interrupt - occurrence of an external disturbance

  • after servicing the interrupt, the 8085 uP resumes its normal working sequence
  • interrupt allows the uP to respond to external events and handles them in a prioritized manner
  • in response to INTR, it generates INTA signals
• the 8085 uP supports the 5 hardware interrupts:

  INTR

  RST 5.5

  RST 6.5

  RST 7.5

  TRAP
• Serial I/O control group

  • data transfers red on D0 - D7 lines in parallel data
  • under some conditions, it is used signal data transfer
  • serial data is entered through SID (serial input data) input received
  • serial data is outputted through SOD (serial output data) input ssend
• Registers:

  Stack pointer

  instruction register

  temporary register

  flag register
• Stack pointer


  -- used to point the memory location of the stack
• stack


  -- sequence of memory locations in the r/w memory

  -- used to store return address during subroutine calls as well as location variables and other data
• instruction register


  holds the operation code (op-code) of the current instruction of a program during an arithmetic/logical operations
• temporary register


  -- an 8-bit register

  -- during an arithmetic and logical operations, one operand is available in A and always transferred in the temporary register
• flag register


  -- an 8-bit register that contains several flags that indicates the status of certain conditions after arithmetic and logical operations
• the flags are as follows: 5

  the zero flag

  the carry flag

  the sign flag

  the parity flag

  the auxiliary flag
• zero flag

  records if the arithmetic and logical operations produced a zero result
• carry flag

  records if the arithmetic and logical operations produced a carry (ex: an extra bit beyond the standard 8-bit)
• sign flag

  records if the sign bit of the result indicating the result was negative sign (sign bit 1) or non-negative (sign bit 0)
• parity flag

  records whether the number 1's in the result is even or odd
• parity flag: even ---- 1

  odd ---- 0
• auxiliary flag


  records if the operation caused a carry after the first four bits
• Vcc

  power supply voltage pin (+5v)
• A0 - A15

  address bus pins for transmitting data between the uP and external memory or I/O devices
• RD

  Read control signal, activated by the uP to initiate to a read operation
• WR

  write control signal, activated by the uP to initiate a write program
• /RESET

  active-low reset input used to reset the uP to its initial state
• /INT

  active-low interrupt input, used for external hardware interrupts
• IO/M

  input/output memory control signal used to distinguish between I/O and memory operation
• SO and SI

  status output pins that indicate the current operating mode of the uP
• HLDA

  hold acknowledge output, used to indicate that the uP has recognized the HOLD request
• HOLD


  Hold input, used to halt the uP operation temporarily
• Addressing Mode in 8085

  -- immediate addressing mode

  -- register addressing mode

  -- direct addressing mode
• immediate addressing mode


  the operand is directly specified in the instruction itself
• register addressing mode


  operand is specified is one of the registers of the microprocessor
• direct addressing mode


  operand is specified by a memory address directly
• indirect addressing mode


  operand is specified indirectly through a register pair usually a HL. The contents of the specified register pair acts a memory address
• register indirect with displacement addressing mode


  operand is specified by adding an 8-bit signed displacement value to the contents of a register pair. the resulting sum is treated as memory address
• immediate indirect addressing mode


  operand is specified indirectly through an immediate value. the immediate value is added to the program counteer and the resulting sum acts as the memory address
• 8085 uP Instruction Format

  -- opcode (1-byte)