Numeric Data Processor (8087)
The 8087 offers numeric data formats and arithmetic operations that
conform to the IEEE Microprocessor Floating Point Standard. All the
proposed IEEE floating point algorithms, exception detection and
handling, infinity arithmetic, and rounding controls are implemented.
The 8087 typically offers a hundredfold improvement in throughput
over calculations done entirely in software routines executed by the
V20. The chip also offers square root, modulus, tangent, arctangent,
logarithm, exponential, scale power, and extract power register
operations. Memory or register operations also include compare, add,
subtract, subtract reversed, multiply, divide, and divide reversed.
These operations are executed by the 8087 in a multiprocessing
environment where both the V20 and 8087 processors execute from a
single instruction stream.
Both processors operate in unison by
monitoring the same instruction stream and executing selected
instructions from it. For example, while the V20 deals with memory
segmentation, calculating the addresses of operands in memory, the
8087 can go off and perform complex arithmetic and logic operations
that would otherwise have to be computed by the V20 software
subroutines.
The 8087 monitors the instruction stream as it appears on the local
bus that is shared with the V20. When one of a particular set of
escape instructions appears, the 8087 automatically recognizes it as its
own. If the escape instruction references memory, the V20 CPU
calculates the memory address for the initial operand and puts that on
the bus to perform a "dummy read." The 8087 latches this address,
reads the operand requested by the CPU (which the CPU ignores),
and begins to execute the required numerical operation. This leaves
the microprocessor free to process nonnumeric commands. The 8087
takes control of the bus only when necessary, to load and store
operands.
The exact procedure is explained in "Coprocessor
Interface" on page 7-7.
7-2
Содержание ZT 8809A
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