Motorola 56000

The Motorola DSP56000 (also known as 56K) is a family of digital signal processor (DSP) chips produced by Motorola Semiconductor (later Freescale Semiconductor then NXP) starting in 1986 with later models are still being produced in the 2020s. The 56k series was quite popular for a time in a number of computers, including the NeXT, Atari Falcon030 and SGI Indigo workstations all using the 56001. Upgraded 56k versions are still used in audio equipment, radar systems, communications devices (like mobile phones) and various other embedded DSP applications. The 56000 was also used as the basis for the updated 96000, which was not commercially successful. The DSP56000 uses fixed-point arithmetic, with 24-bit program words and 24-bit data words. It includes two 24-bit registers, which can also be referred to as a single 48-bit register. It also includes two 56-bit accumulators, each with an 8-bit "extension" (aka headroom); otherwise, the accumulators are similar to the other 24/48-bit registers. Being a Modified Harvard architecture processor, the 56k has three memory spaces+buses (and on-chip memory banks in some of the models): a program memory space/bus and two data memory space/bus. 24 bits was selected as the basic word length because it gave the system a reasonable number range and precision for processing audio (sound), the 56000's main concern. 24 bits correspond to a large 144 dB dynamic range, sufficient in the 1980s when analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) rarely exceeded 20 bits. One example is ADSL applications, where filters typically require 20 bits of accuracy. The leftmost four bits are considered ample headroom for calculations. The processor is capable of carrying out 16.5 Million Instructions Per Second (MIPS) at the maximum specified clock speed of 33 MHz, and has hardware support for block-floating point FFT. It uses 5 V TTL levels and consumes approximately 0.4 W. In most designs the 56000 is dedicated to one single task, because digital signal processing using special hardware is mostly real-time and does not allow any interruption.