An Implementation of Picoblaze 8bit Microcontroller in Verilog

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An Implementation of Picoblaze 8-bit
Microcontroller in Verilog

• CS497 Presentation
• Supervised by Dr. Shashank K. Mehta
• Presented by Abhinav S. Bhatele (Y1008)

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Introduction

• Constant(k) Coded Programmable State Machine
  (KCPSM) developed by Xilinx
• It is a 8-bit fully embedded microcontroller
• It has 8 16-bit registers, ALU, 256 I/O ports,
  15-location CALL/RETURN stack
• It also has facility for reset and interrupt
• Instruction size is 16-bits

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Constant(k) Coded machine

• Constant values are specified for use in the
  following aspects of a program
• Constant data value for use in an ALU operation
• Constant port address to access a specific piece
  of information or control logic external to the
  PicoBlaze module
• Constant address values for controlling the
  execution sequence of the program
• Constant Cycles
• All instructions under all conditions execute
  over two clock cycles.
• Constant Program Length
• The program length is 256 instructions

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Microcontroller Diagram
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Details

• Registers
• 16 8-bit registers labelled from s0 to sF
• ALU
• Takes two operands of 8-bits and returns the
  result to the first register
• Add, Subtract with and without a carry are
  supported
• LOAD, AND, OR and XOR
• Flow Control
• Zero and Carry flags are set by the ALU
  operations
• CALL/RETURN used for subroutine facilities

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Details (contd.)

• Reset
• Processor goes back to initial state
• Starts executing from address 00
• Everything except the registers is reinitialized
• Input/Output
• During an input the value on the indicated port
  is transferred to one of the registers
• During an output the value from one of the
  registers is written on an output port
• Interrupt
• A single interrupt is allowed

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Use of the available VHDL Code

• Code divided into modules which were instantiated
  and used by the main module
• Code of individual modules uses pre-defined
  libraries like unisim
• We looked at the instantiations in the main
  module and the connections between them
• Port mapping of signals and wires to various
  modules helped us arrive at the datapath

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Lets see how ??

• The next problem to figure out what these boxes
  do ?
• To do this we need to look at the instruction set
  first

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Instruction Set

• Program Control Group
• Jump Instruction Both conditional and
  unconditional
• Call Instruction

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• Program Control Group
• Return Instruction

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Interrupt Group

• ReturnI
• Enable and Disable Interrupt

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Logical Group

• LOAD
• AND

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Logical Group (contd.)

• OR
• XOR

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Arithmetic Group

• ADD without carry
• ADDC - with carry

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Arithmetic Group (contd.)

• SUB without carry
• SUBC with carry

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Shift and Rotate Group

• Shift right
• Shift left

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Shift right
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Shift left
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Input and Output Group

• Input
• Output

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Individual Modules

• Operand Select
• Arithmetic Group
• Logic Group
• Shift and Rotate Group
• ALU Multiplexer
• ALU Control
• Program Counter
• Stack Counter

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Conclusion

• The latest assembler (an executable) gives the
  verilog file for a program written in this
  instruction set
• A module of the Program ROM is used together with
  the processors main module
• Together they define the complete microcontroller
  

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THANK YOU !!