The 8 bit control unit.

Notes

• Review the microcode for the 8-bit computer
• Ben builds a microcontroller
  • This has a μpc - from a counter (74x161)
  • An eeprom containing the microcode (two 28c16 chips)
• The &mupc; steps each clock cycle
• Each clock cycle, a μinstruction is fetched from the eeprom
• The address of the μinstruction is
  • The op-code for the instruction to be executed (in ir 4-7)
  • The μpc (3 bits).
• 
• The bits of the microinstruction power the individual lines to the different functional units of the pc.
• The μinstruction:
  • 7 bit address (ir[4..7],μpc)
  • His code to write to the eeprom
    • HLT MI RI RO IO II AI AO EO SU BI OI CE CO
    • 
    • His entire instruction code:
    • 
  • Note all instructions start with Fetch
    • IR XXXX μpc 0000 : MI|CO
    • IR XXXX μpc 0001 : RO|II|CE

      HLT MI RI RO IO II AI AO EO SU BI OI CE CO
       0  1  0  0  0  0   0  0  0  0  0  0  0  1
       0  0  0  1  0  1   0  0  0  0  0  0  1  0 

  • This video shows doing this.
  • Look at about 22:08 for the final functioning machine.
  • Note the control word in the lower right hand corner.
  •