Texas Instruments Corporation

Wanda K Gass

Surendar S Magar

Edward R Caudel

A digital data processing system employs a single-chip microcomputer device having separate on-chip program and data memory, executing instructions in a single machine state. An external program address bus allows off-chip program fetch in a memory expansion mode, with the opcode returned by an external data bus, or all program storage can be off-chip in a system emulator mode. The ALU and accumulator have 32-bit data paths, while the busses are 16-bit. Various test modes are permitted; for example, the internal program ROM may be read out on the data bus, one opcode at a time, for test purposes without executing the opcodes. Alternatively, the internal data RAM may be disabled and an external RAM used, for which a three-state or four-state instruction execution sequence is established instead of one per state to allow an operand to be transferred in on the data bus and high and low words of the accumulator transferred out; this node is very useful for checking ALU operations not otherwise accessible off-chip.

Microcomputer device having test mode substituting external RAM for

A system for real-time digital signal processing employs a single-chip microcomputer device having separate on-chip program ROM and data RAM, with separate address and data paths for program and data; however, the accumulator in the data path may be used as a program address source. An external program address bus allows off-chip program fetch in an expansion mode, with the opcode returned by an external data bus. A bus interchange module allows transfer between the separate internal program and data busses. The internal busses are 16-bit, while the ALU and accumulator are 32-bit. A multiplier circuit produces a single state 16.times.16 multiply function separate from the ALU, with 32-bit output to the ALU. One input to the ALU passes through a 0-to-15 bit shifter with sign extension. A separate shift or offset is provided in coupling the output of the accumulator to an internal data bus for use in scaling when storing the accumulator contents in internal data RAM specified by instructions. Also, the RAM itself has an internal shift function used in convolution.

Microcomputer with offset in store-accumulator operations

A system for real-time digital signal processing employs a single-chip microcomputer device having separate on-chip program ROM and data RAM, with separate address and data paths for program and data; however, the accumulator in the data path may be used as a program address source for table look-up, for example. An external program address bus allows off-chip program fetch in an expansion mode, with the opcode returned by an external data bus. A bus interchange module allows transfer between the separate internal program and data busses in special circumstances, such as accumulator addressing. The internal busses are 16-bit, while the ALU and accumulator are 32-bit. A multiplier circuit produces a single state 16.times.16 multiply function separate from the ALU, with 32-bit output to the ALU. One input to the ALU passes through a 0-to-15 bit shifter with sign extension. The contents of the accumulator may be forced to a maximum or minimum value upon overflow or underflow to simulate saturation in analog systems; this function may be enabled or disabled under instruction control.

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Wanda K Gass