A register is an
electronic device that holds a
binary number. One can be constructed from a bank of
flip-flops arranged in a
parallel load or
serial load configuration, or both. Similarly, a register may be read from in
parallel or
serial, or both. An example of a simple 4-bit parallel in/parallel out register is shown here:
Assembly: Whole Unit:
+---+ +-+
I3----|D Q|--O3 | |
+-|> | I--/--|C|--/--O
| +---+ 4 | | 4
| +---+ | |
I2--|-|D Q|--O2 +-+
+-|> |
| +---+
| +---+
I1--|-|D Q|--O1
+-|> |
| +---+
| +---+
I0--|-|D Q|--O0
clk-+-|> |
+---+
The 'C' in the Whole Unit diagram is simply a name for this register and the '4' indicates that there is a 4-bit bus on both the input and output.
See also shift register (for a serial load configuration), accumulator, three-state logic, arithmetic logic unit, sequential arithmetic, D Flip-Flop, SR Flip-Flop, JK Flip-Flop.