Specifications

Numeric Data Processor (8087)
OPERATION
The following description is an overview of NDP operation. See the
reference section at the end of this chapter for sources with more
detailed explanations.
Coprocessor
Interface
Instruction Level Support
The purpose of the NDP is to extend the math capabilities of the V40.
This includes instruction level support for high-precision integer and
floating point data types with operations such as add, subtract,
multiply, divide, square root, exponent, logarithmic, and trigono-
metric. For the programmer, the NDP adds 68 numerical instructions
and seven data types to the V40 instruction set. The instructions are
referred to as ESCAPE instructions because they include an ESCAPE
prefix. The ESCAPE prefix signals the V40 and the NDP that a
numeric instruction is to be executed.
The NDP maintains a copy of the V40 instruction queue. Instructions
fetched by the V40 are also monitored by the NDP. The NDP checks
the first byte of each instruction looking for an ESCAPE prefix. If the
first byte is not an ESCAPE prefix, the NDP ignores the instruction.
If the first byte of an instruction is an ESCAPE prefix, the NDP
decodes the numeric instruction in parallel with the V40.
An NDP numerical instruction has one of three options:
1. No reference to memory
2. Read operand from memory
3. Write operand to memory
If no reference to memory is needed, the NDP executes the
instruction. If the instruction includes a reference to memory, the V40
executes a "dummy read" cycle, so called because the V40 ignores the
data read. Because the NDP does not include an address generator, it
must depend on the V40 to generate the operand starting address.
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