The NEC μPD7720 is the name of fixed point

digital signal processor A digital signal processor (DSP) is a specialized microprocessor chip, with its architecture optimized for the operational needs of digital signal processing. DSPs are fabricated on metal–oxide–semiconductor (MOS) integrated circuit chips. ...

s from

NEC is a Japanese multinational information technology and electronics corporation, headquartered at the NEC Supertower in Minato, Tokyo, Japan. It provides IT and network solutions, including cloud computing, artificial intelligence (AI), Inte ...

(currently

Renesas Electronics is a Japanese semiconductor manufacturer headquartered in Tokyo. The name "Renesas" is a contraction of "Renaissance Semiconductor for Advanced Solutions." The company was established in 2002 as Renesas Technology through the merger of the semi ...

). Announced in 1980, it became, along with the

Texas Instruments Texas Instruments Incorporated (TI) is an American multinational semiconductor company headquartered in Dallas, Texas. It is one of the top 10 semiconductor companies worldwide based on sales volume. The company's focus is on developing analog ...

TMS32010, one of the most popular DSPs of its day.

Background

In the late 1970s, telephone engineers were attempting to create technology with sufficient performance to enable digital touch-tone dialing. Existing digital signal processing solutions required over a hundred chips and consumed significant amounts of power.

Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, and Delaware General Corporation Law, incorporated in Delaware. Intel designs, manufactures, and sells computer compo ...

responded to this potential market by introducing the

Intel 2920 Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, and incorporated in Delaware. Intel designs, manufactures, and sells computer components such as central processing ...

, an integrated processor that, while it had both digital-to-analog and analog-to-digital converters, lacked additional features (such as a hardware multiplier) that would be found in later processors. Announcements for the first "real" DSPs, the NEC μPD7720 and the Bell Labs DSP-1 chip, occurred the following year at the 1980

IEEE The Institute of Electrical and Electronics Engineers (IEEE) is an American 501(c)(3) organization, 501(c)(3) public charity professional organization for electrical engineering, electronics engineering, and other related disciplines. The IEEE ...

International Solid-State Circuits conference. The μPD7720 first became available in 1981 and commercially available in late 1982 at a cost of ¥20.000 (around $82 and inflation corrected for 2023 dollars around $304). Beyond their initial use in telephony, these processors found applications in disk drive and graphics controllers, speech synthesis and modems.

Architecture

Detailed descriptions of the μPD7720 architecture are found in Chance (1990), Sweitzer (1984) and Simpson (1984). Briefly, the NEC μPD7720 runs at 4 MHz frequency with 128-word 16-bit data RAM, 512-word 13-bit data ROM, and 512-word 23-bit program memory, which has

VLIW Very long instruction word (VLIW) refers to instruction set architectures that are designed to exploit instruction-level parallelism (ILP). A VLIW processor allows programs to explicitly specify instructions to execute in parallel computing, para ...

-like instruction format, enabling all of ALU operation, address register increment/decrement operation, and move operation in one cycle. The stack area, which is distinct from the main memory address space, is allocated in a separate address space. The stack, utilized during

subroutine In computer programming, a function (also procedure, method, subroutine, routine, or subprogram) is a callable unit of software logic that has a well-defined interface and behavior and can be invoked multiple times. Callable units provide a ...

calls and

interrupt In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted ...

s, has a depth of four.

Variants

The NEC μPD77C25, which succeeded the μPD7720, runs at 8 MHz frequency with 256-word 16-bit data RAM, 1,024-word 16-bit data ROM, and 2,048-word 24-bit program memory. The stack, utilized during subroutine calls and interrupts, maintains the same depth of four as that of the μPD7720.
NEC μPD77C25 was succeeded by backwards compatible μPD96050 which runs at either 10 or 15 MHz frequency with 2,048 16-bit data RAM, 2,048-word 16-bit data ROM, and 16,384-word 24-bit program memory. Compared to its predecessor, call stack has been expanded to depth of 8, instruction set includes some additional instructions and it supports battery backup for data RAM.
Both μPD77C25 (DSP-1, DSP-2, DSP-3, DSP-4) and μPD96050 (ST010, ST011) were used as enhancement coprocessors in Super NES game cartridges.

References

External links

* Datasheets for the UPD7720A, UPD7720AC and UPD7720AD are availabl
here
* Datasheets for the UPD77C25C, UPD77C25GW and UPD77C25L are availabl

{{Renesas Electronics muPD07720 Digital signal processors