Microprocessor ALU with absolute value function
AssigneeTexas Instruments Incorporated
InventorKarl M. Guttag
Life of this patent
Estimating the term…
Abstract
A single-chip microprocessor device of the MOS/LSI type contains an ALU, several internal busses, a number of address/data registers, and an instruction register with associated control decode or microcontrol generator circuitry. The device communicates with external memory and peripherals by a bidirectional multiplexed address/data bus and a number of control lines. The ALU circuit is constructed to modify the carry-generate term so that the twos-complement function (and others) can be generated for either of the ALU inputs. By then connecting the most significant bit of the input to the arithmetic/logic control of the ALU, the absolute value function is generated. This results in faster signed multiply and divide instructions with less circuitry.
Claims6
An arithmetic logic unit for a microprocessor, such unit including a plurality of parallel stages, each stage comprising:
- a first single-bit ALU input,
- a second single-bit ALU input,
- a single-bit carry-in input from a prior one of said stages,
- a single-bit carry-out output to a next one of said stages,
- a plurality of control lines for defining an operation performed in said arithmetic logic unit,
- first logic means connected to receive said first and second inputs and responsive to said control lines for producing a carry propagate term output,
- second logic means connected to receive said first and second inputs and responsive to said control lines for producing a carry generate term output,
- third logic means providing an Exclusive NOR function and having first and second NOR inputs and an ALU output, the first NOR input being conditionally coupled to said carry generate term output through fourth logic means and also responsive to one of said control lines, the second NOR input being coupled to said carry propagate term output,
- and said fourth logic means coupled to said first NOR input and to said carry generate term output being responsive to one other of said control lines.
Dependencies are inferred from the claim text.