Fulfill your Atari's G-Spot with an FPU for that "Duo-Core" Experience

Atari FPU Coprocessor Motorola 68881 68882After 20 years of the same old, same old, even the most intimate relationships can get a little boring.  Perhaps it's time you spiced up your love life by learning how to fulfill your Atari's G-Spot! Here's how:

Atari Mega STe, TT, and Falcon computers running on a Motorola 68020 and 68030 CPU are designed for use with an optional floating point unit (FPU) - the Motorola 68881 or newer, much improved 68882 coprocessor.  Also known as a math coprocessor, this extra chip accelerates your Atari's performance by offloading processor-intensive tasks such as floating point arithmetic, graphics, signal processing, string processing, Savitsky-Golay derivation, or encryption.  For musicians, this means faster audio processing and quicker refresh rates on Cubase Audio and other music and MIDI applications that are programmed to utilize this chip. You can think of it as an "almost duo-core" machine!

How it Works

All Motorola 68020 and 68030 CPUs reserve the "F-line" instructions — that is, all opcodes (numeric instructions) beginning with the hexadecimal digit "F" act as traps (interupt signals) that hand control to the computer's operating (OS) system.  If a 68882 is present in the system, the OS diverts these instructions for execution. If not, the OS will either call an FPU emulator to execute the instruction using 68020/68030 integer-based software code, or returns an error code to the program.

The 68882 FPU has 8 directly addressable 80-bit registers. It supports seven data types: 8-bit, 16-bit and 32-bit integers, as well as single, double and extended-precision floating point numbers, and packed decimal strings, as defined by the IEEE floating-point standard (IEEE 754). It is designed specifically for floating-point math and is not a general-purpose CPU. When an instruction requires any address calculation, for example, the 68882 will ask the main CPU to do the calculation.

The Motorola 68882 is an improved version of the 68881, executing some instructions 40% faster, with better pipelining, and available at higher clock speeds up to 50MHz. The 68882 FPU also executes more than one floating-point instruction at the same time and uses a faster conversion method of external operands to/from FPU's internal format.

To get maximum performance from the newer 68882 co-processor, the software needs to be re-compiled. This way, the 68882 may run re-compiled software up to two times faster than the older 68881. Performance gain for older applications compiled for the 68881 is usually is not as impressive - the 68882 may only run these programs up to 15 - 25% faster.

When the Motorola 68040 processor was introduced, it included the FPU on board. Most instructions and numeric representation modes from the 68882 were supported in hardware, but some were not, and were emulated through a software package.  Unfortunately, this processor was intended for the Atari Sparrow FX-1 which never made it to production.

Atari-Motorola-68882-68881-68030-Coprocessor.jpgWhat FPU should I use in my Falcon?

The Atari Falcon030 works natively with a basic 68882 16MHz FPU because the Falcon's system bus runs at this rate. Nevertheless, it is recommended you use the 33MHz (68882-fn33) version as it is prone to less pin glitches and gives a 1MHz overhead.  Since the FPU is an is an asynchronous device (independant of the CPU's speed), faster chips up to 50MHz will "work" but only at 16MHz unless you over-clock it by installing a separate clock source.  Even still, the difference will be minor since the system bus still has to catch up while running at 16MHz.  This is why most Falcon accelerator cards bypass the system bus entirely.

Motorola MC68882 FPU Stats and Facts

MC68882 16MHz version (info unavailable)
MC68882 25MHz version runs at 264 Kflops
MC68882 33MHz version runs at 352 Kflops
MC68882 40MHz version runs at 422 Kflops
MC68882 50MHz version runs at 528 Kflops

  • The Mega STe was intended for use with the 68881 but has been reported to work with the 16Mhz 68882
  • There were some alleged FPU expansion cards made for the Atari ST, STe, and MEGA ST however the 68000 CPU could not make use of it without additional software support
  • The FPU IC socket is designed to fit with PLCC format chips only.


Compatible Atari Music Software for the Motorola MC68882 Coprocessor

Music software that can use the 68882:

  • Aniplayer (only for Real Audio 28.8K and some Shared Library .SLB)
  • Audiomaster (Soundpool CD writer)
  • Blade Encoder (MP3 Encoder recommended for MinT)
  • Dynamikprozessor (Soundpool?)
  • Dynamite mastering tools with Denoiser/ Equaliser and Dynamics (Soundpool)
  • FalcAMP (150% faster on Falcon)
  • Studio Son (two versions available for single 68030 CPU or 68030 CPU + 68882 FPU)
  • V-Trax (two versions available for single 68030 CPU or 68030 CPU + 68882 FPU)
  • Zero-X (three versions available: 68000 for the STe, single 68030 CPU or 68030 CPU + 68882 FPU for the TT or Falcon)
  • Cubase Audio Falcon

Music software that must use the 68882:

  • Csound (programming language to create sounds)
  • Lame Encoder (for MinT)
  • Lame Encoder TOS version (for TOS & MagiC)
  • Mpg123 (MP3 Player)
  • abcm2ps, abctab2ps and abcMIDI (for FreeMINT/EasyMINT)

One should assume there are dozens of ommissions in the above list. If you know of more FPU compatible music programs, please contact This e-mail address is being protected from spambots. You need JavaScript enabled to view it . Community input is appreciated.

To find out if your Atari already has a coprocessor installed, download SYSINFO 8.34