MOTOROLA M68020 USER’S MANUAL 9- 1
SECTION 9
APPLICATIONS INFORMATION
This section, which provides guidelines for using the MC68020/EC020, contains
information on floating-point units, byte select logic, power and ground considerations,
clock driver, memory interface, access time calculations, module support, and access
levels.
9.1 FLOATING-POINT UNITS
Floating-point support for the MC68020/EC020 is provided by the MC68881 floating-point
coprocessor or the MC68882 enhanced floating-point coprocessor. Both devices offer a
full implementation of the
IEEE Standard for Binary Floating-Point Arithmetic
(754). The
MC68882 is a pin- and software-compatible upgrade of the MC68881, with an optimized
MPU interface that provides over 1.5 times the performance of the MC68881 at the same
clock frequency.
Both coprocessors provide a logical extension to the integer data processing capabilities
of the main processor. They contain a high-performance floating-point arithmetic unit and
a set of floating-point data registers that are utilized in a manner that is analogous to the
use of the integer data registers of the processor. The MC68881/MC68882 instruction set,
a natural extension of all earlier members of the M68000 family, supports all addressing
modes and data types of the host MC68020/EC020. The programmer perceives the
MC68020/EC020 coprocessor execution model as if both devices are implemented on
one chip. In addition to supporting the full IEEE standard, the MC68881 and MC68882
provide a full set of trigonometric and transcendental functions, on-chip constants, and a
full 80-bit extended-precision real data format.
The interface of the MC68020/EC020 to the MC68881 or MC68882 is easily tailored to
system cost/performance needs. The MC68020/EC020 and the MC68881/MC68882
communicate via standard asynchronous M68000 bus cycles. All data transfers are
performed by the main processor at the request of the MC68881/MC68882; thus, memory
management, bus errors, address errors, and bus arbitration function as if the
MC68881/MC68882 instructions are executed by the main processor. The floating-point
unit and the processor can operate at different clock speeds, and up to seven floating-
point coprocessors can simultaneously reside in an MC68020/EC020 system.
Figure 9-1 illustrates the coprocessor interface connection of an MC68881/MC68882 to an
MC68020/EC020 (uses entire 32-bit data bus). The MC68881/MC68882 is configured to
operate with a 32-bit data bus when both its A0 and
SIZE pins are connected to V
CC
.
Refer to the MC68881UM/AD,
MC68881/MC68882 Floating-Point Coprocessor User's
Manual
, for configuring the MC68881/MC68882 for smaller data bus widths.
To Next Page
Loading...
Need help?
General
