In the late 1970s, telephone engineers were attempting to create technology with sufficient performance to enable digital touch-tone dialing.[1] Existing digital signal processing solutions required over a hundred chips and consumed significant amounts of power.[2]Intel responded to this potential market by introducing the Intel 2920,[3] 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.[1] Announcements for the first "real" DSPs, the NEC μPD7720 and the Bell Labs DSP-1 chip, occurred the following year at the 1980 IEEE International Solid-State Circuits conference.[4] The μPD7720 first became available in 1981[5] and commercially available in late 1982 at a cost of ¥20.000 (around $82 and inflation corrected for 2023 dollars around $304).[6] Beyond their initial use in telephony, these processors found applications in disk drive and graphics controllers, speech synthesis and modems.[7]
Detailed descriptions of the μPD7720 architecture are found in Chance (1990),[8] Sweitzer (1984)[9] and Simpson (1984).[10] 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-like instruction format, enabling all of ALU operation, address register increment/decrement operation, and move operation in one cycle.[11] The stack area, which is distinct from the main memory address space, is allocated in a separate address space. The stack, utilized during subroutine calls and interrupts, has a depth of four.[12]
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.[13] The stack, utilized during subroutine calls and interrupts, maintains the same depth of four as that of the μPD7720.[13]
^Chance, R. J. (1990). "Devices Overview". In Jones, N. B.; Watson, J. D. McK. (eds.). Digital Signal Processing: Principles, Devices and Applications. Peter Peregrinus Ltd. pp. 10–12. ISBN0863412106.
^Sweitzer, S. (March 1984). "A low cost FFT chip set". ICASSP '84. IEEE International Conference on Acoustics, Speech, and Signal Processing. Vol. 9. pp. 371–373. doi:10.1109/ICASSP.1984.1172726.(subscription required)
^Simpson, Robert J.; Terrell, Trevor J. (September 1984). "Digital filtering using the NEC μPD7720 signal processor". Microprocessing and Microprogramming. 14 (2): 67–78. doi:10.1016/0165-6074(84)90101-7.(subscription required)
