Micro Programmed Control Unit

Micro Programmed Control Unit

• 1.
  Introduction Types Comparison Control Memory Address Sequencing Microinstruction format and Description Control Unit
• 2.
  Introduction  CU isthe engine that runs the entire computer with the help of the control signals.  It perform the correct sequencing of the correct signals.  It controls everything with a few control signals that points within processor and a few control signals to the system bus.
• 3.
  Introduction  All themicro-operation are controlled by CU by performing two basic tasks:  Sequencing: It causes the processor to step through the series of micro-operation in proper sequence, based on program being executed.  Execution: It causes each micro-operation to be performed.
• 5.
  Control Signal Sources Clock  It helps to synchronize the operation. It causes one micro- operation to be performed for each clock pulse  Instruction Register  Op-code for current instruction  Determines which micro-instructions are performed  Flags  State of CPU  Results of previous operations
• 6.
  Control Signal Sources From Control Bus  Interrupts / Bus Requests  Acknowledgements
• 7.
  Control Signal Outputs Within Processor  Cause data movement  Activate specific functions  Via Main Bus  To memory  To I/O modules
• 8.
  Types  There aretwo design approach for CU:  Hardwired approach  Micro-programming approach
• 9.
  Hardwired Approach  Thecontrol signals are generated by the help of the hardware.  It can be designed as the clock sequential circuit.  It is implemented with logic gates, flip-flops, decoders, multiplexers and other logic buildings blocks.
• 10.
  Micro programmed Approach All controls that can be activated simultaneously are grouped together to form the control words.  These words are stored in the control memory.  The control words are fetched from the control memory and are routed to various functional units to enable appropriate processing hardware.
• 11.
  Comparison Attributes Hardwired ControlMicroprogramming Control Speed Fast Slow Cost of Implementation More Cheaper Flexibility Difficult to modify Flexible Ability to handle complex instruction Difficult Easier Decoding Complex Easy Application RISC CISC Instruction Set Size Small Large Control Memory Absent Present
• 12.
  Micro programmed ControlUnit
• 13.
  Control Unit Function Sequence login unit issues read command  Word specified in control address register is read into control buffer register  Control buffer register contents generates control signals and next address information  Sequence login loads new address into control buffer register based on next address information from control buffer register and ALU flags
• 14.
  Next Address Decision Depending on ALU flags and control buffer register  Get next instruction  Add 1 to control address register  Jump to new routine based on jump microinstruction  Load address field of control buffer register into control address register  Jump to machine instruction routine  Load control address register based on opcode in IR
• 15.
  Control Memory Organization
• 16.
  Functioning of Microprogrammed Control Unit
• 17.
  Selection of addressfor control memory
• 19.
  Conditional Branching
• 20.
  Mapping of Instructions
• 21.
  Mapping of Instructionsto Microroutines
• 22.
  Machine Instruction Format