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Circuit Description

A demonstration of the RTLIB user-defined ALU. This simulation component models a multi-function arithmetic-logic unit with user-selectable bit-width and a variety of functions. The mapping from the function-select input to actual ALU operation can be selected via the property-sheet.

Open the ALU dialog (popup-menu, edit-component) to select the bit-width and the operation mapping of the ALU. Just select a new operation from the pulldown-menu of each function opcode to change the behaviour of the ALU. The following image shows the default mapping used in this applet:

For example, the value function=9 selects the basic addition A+B, while function=11 selects the A+B+Cin addition with separate carry-input, and function=15 selects the bitwise logical A OR B operation.

Besides the main n-bit result value, the ALU also provides five single-bit outputs: carry-out, zero, negative (two's-complement), A=B (A equals B), and OVERFLOW.