Flip-flops can be connected to act as a register

1
A register design with parallel load input

• Flip-flops can be connected to act as a register
• At the input, a mux selects a new input or
  retains the old value
• All flip-flops get the same clock cycle
• LD signal one means load new value
• LD signal zero means retain old value

2
Multiple registers

• In a system we can have more than one register
• For an operation we can select any of the
  registers
• Each register can be loaded or old value can be
  retained
• A register can be selected for output
• There can be more than one set of multiplexers at
  the output

3
Connecting registers to ALU

• A set of registers with selection signals can
  produce two outputs
• These outputs can be connected to ALU input
• A 4-function ALU receives two inputs and produces
  one output
• It needs two select bits to selects function
• Needs LD1, and LD2 signals, M1 and M2 signal

4
Writing result back to registers

• Output of ALU may have to be written in registers
• Registers may also get data from somewhere else
  like keyboard
• Therefore we need to select data to be written to
  register file
• This requires another multiplexer
• Or we can use a bus