The Motorola 68881 was a floating-point coprocessor chip that was utilized in some computer systems that used the 68020 or 68030 CPU. The addition of the 68881 chip added substantial cost to the computer, but added a floating point unit that could rapidly perform floating point math calculations. At the time, this was useful mostly for scientific and mathematical software. Motorola 68020 The Motorola 68020 is a microprocessor from Motorola. ... Motorola 68030 Processor from a Macintosh IIsi The Motorola 68030 is a 32-bit microprocessor in Motorolas 68000 family. ... This CPU uses numerous pins to connect to the motherboard. ... A floating point unit (FPU) is a part of a CPU specially designed to carry out operations on floating point numbers. ... A floating-point number is a digital representation for a number in a certain subset of the rational numbers, and is often used to approximate an arbitrary real number on a computer. ...

Overview

The 68020 and 68030 CPUs were designed with the separate 68881 chip in mind. Their instruction sets reserved the "F-line" instructions — that is, all opcodes beginning with the hexadecimal digit "F" were "traps" which would throw an interrupt, handing control to the computer's operating system. If a 68881 were present in the system, the CPU would allow it to execute the instruction. If not, the OS would either call an FPU emulator to execute the instruction using 68020 integer-based software code, or would return an error code to the program. A computer can perform operations, each of which is assigned a numeric code called an opcode. ... In mathematics and computer science, hexadecimal or simply hex is a numeral system with a radix or base of 16 usually written using the symbols 0–9 and A–F or a–f. ... In computer science, an interrupt is a signal from a device which typically results in a context switch: that is, the processor sets aside what its doing and does something else. ... In computing, an operating system (OS) is the system software responsible for the direct control and management of hardware and basic system operations. ... This article is about emulation in computer science. ...

The 68881 had eight 80-bit data registers. It allowed seven different modes of numeric representation, including single-precision, double-precision, and extended-precision, as defined by the IEEE floating-point standard, or "IEEE 754". It was designed specifically for floating-point math and was not a general-purpose CPU. For example, when an instruction required any address calculations, the main CPU would handle them before the 68881 took control. The IEEE Standard for Binary Floating-Point Arithmetic (IEEE 754) is the most widely-used standard for floating-point computation, and is followed by many CPU and FPU implementations. ...

The CPU/FPU pair were designed such that both could run at the same time. When the CPU encountered a 68881 instruction, it would hand the FPU all operands needed for that instruction, and then the FPU would release the CPU to go on and execute the next instruction.

The Motorola 68882 was an improved version of the 68881, with better pipelining, and eventually available at higher clock speeds. Its instruction set was exactly the same as that of the 68881. Motorola claimed in some marketing literature that it executed some instructions 40% faster than a 68881 at the same clock speed, though this did not reflect typical performance at all. In synchronous digital electronics, such as most computers, a clock signal is a signal used to coordinate the actions of two or more circuits. ...

Notable computers including 68881 or 68882 FPUs included the Sun 3 from Sun Microsystems, the Macintosh II family of computers from Apple Computer, and the Commodore Amiga 3000. Some third-party Amiga products used the 68881/2 as a memory-mapped peripheral to the 68000. Sun Microsystems is a computer, semiconductor and software manufacturer headquartered in Santa Clara, California, in Silicon Valley. ... Macintosh II was the first personal computer model of the Macintosh II series in the Apple Macintosh line. ... Apple Computer, Inc. ... Commodore is the commonly used name for Commodore International, a West Chester, Pennsylvania based electronics company who was a major player in the 1980s home computer field. ... The A3000, also known as the Commodore Amiga 3000, was a much more serious proposition to build a professional multimedia computer than the previous A2000 effort. ... Memory-mapped I/O (MMIO) and port I/O (also called port-mapped I/O or PMIO) are two complementary methods of performing input/output between the CPU and I/O devices in a computer. ... The Motorola 68000 is a CISC microprocessor, the first member of a successful family of microprocessors from Motorola, which were all mostly software compatible. ...

When the Motorola 68040 processor was introduced, it included the FPU internally. Most instructions and numeric representation modes from the 68881 were supported in hardware, but some were not, and were emulated through a software package. The Motorola 68040 is a microprocessor from Motorola. ...

Selected statistics

68881

• 155,000 transistors on-chip
• 16 MHz version ran at 160 kflops
• 20 MHz version ran at 192 kflops
• 25 MHz version ran at 240 kflops

68882

• 176,000 transistors on-chip
• 25 MHz version ran at 264 kflops
• 33 MHz version ran at 352 kflops
• 40 MHz version ran at 422 kflops
• 50 MHz version ran at 528 kflops

68040

• 25 MHz FPU ran at 3,500 kflops
• 33 MHz FPU ran at 4,662 kflops
• 40 MHz FPU ran at 5,600 kflops

These statistics came from the comp.sys.m68k FAQ. No statistics are listed for the 16MHz and 20MHz 68882, though these chips were indeed produced.

References

• Motorola MC68000 Family Programmer's Reference Manual
• comp.sys.m68k FAQ

List of Motorola/Freescale microprocessors

The 6800 family | 6809 (see also: Hitachi 6309) | 68000 family: 68000 | 68008 | 68010 | 68012 | 68020 | 68030 | 68040 | 68060 | Coldfire | Dragonball | Pre-PPC RISC: 88000 | Floating-point processors: 68881 | 68882 PowerPC family (as part of AIM): PPC 7XX range (aka "PowerPC G3") | PPC 7XXX range (aka "PowerPC G4") Image File history File links The M-logo graphic of the Motorola logo, cropped from Image:Motologo. ... Image File history File links Logo graphic part of Freescale Semiconductor logo, cropped from Image:FreescaleSemiconductor. ... The following is a categorized list of Motorola products; end user appliances, automotive products (Motorola Automotive Group, has a facility in Northbrook, IL), lighting products (Motorola Lighting Inc. ... The 68h family of 8-bit processors is based upon the Motorola 6800 CPU. However not just Motorola produced or innovated on that design. ... The Motorola 6809 is an 8-bit* microprocessor from Motorola, introduced circa 1979. ... The 6309 is Hitachis version of the Motorola 6809 microprocessor. ... The Motorola 680x0/0x0/m68k/68k/68K family of CISC microprocessor CPU chips were 32-bit from the start, and were the primary competition for the Intel x86 family of chips. ... The Motorola 68000 is a CISC microprocessor, the first member of a successful family of microprocessors from Motorola, which were all mostly software compatible. ... The Motorola MC68008 is a 8/16/32-bit microprocessor from the early 1980s. ... The Motorola MC68010 processor is a 16/32-bit microprocessor from Motorola, made in the early 1980s. ... The Motorola MC68012 processor is a 16/32-bit microprocessor from the early 1980s. ... Motorola 68020 The Motorola 68020 is a microprocessor from Motorola. ... Motorola 68030 Processor from a Macintosh IIsi The Motorola 68030 is a 32-bit microprocessor in Motorolas 68000 family. ... The Motorola 68040 is a microprocessor from Motorola. ... The Motorola 68060 is a 32-bit microprocessor from Motorola, and is the successor to the Motorola 68040. ... The Motorola Coldfire is a 68k architecture microprocessor manufactured for embedded systems development by Motorola (now Freescale Semiconductor). ... Motorola Dragonball Microprocessor Motorola/Freescale Semiconductors Dragonball is microprocessor design based on the famous 68000 core, but implemented as an all-in-one low-power solution for handheld computer use. ... The 88000 (m88k for short) is a microprocessor design produced by Motorola. ... The Motorola 68881 was a floating-point coprocessor chip that was utilized in some computer systems that used the 68020 or 68030 CPU. The addition of the 68881 chip added substantial cost to the computer, but added a floating point unit that could rapidly perform floating point math calculations. ... PowerPC is a RISC microprocessor architecture created by the 1991 Apple-IBM-Motorola alliance, known as AIM. Originally intended for workstations, PowerPC CPUs have since become popular embedded and high-performance processors as well. ... AIM was an alliance formed in 1991 between Apple Computer, IBM and Motorola to create a new computing standard based on the PowerPC architecture. ... PowerPC G3 is a designation used by Apple Computer to a third generation of PowerPC microprocessors. ... PowerPC G4 is a designation used by Apple Computer to describe a fourth generation of PowerPC microprocessors. ...