Western Electric 32206 (WE32206) is a Floating Point Unit for
WE 32200 microprocessor family. Like
its predecessor, Western Electric
32106, the WE32206 supports single, double end extended precision
floating-point numbers, it can execute all basic mathematical,
comparison and rounding operations, and read and write data in BCD
and integer formats. All data loaded by the 32206 is converted
internally into extended-precision format, and all further
calculations are performed in this format. The WE32206 includes a few
new transcendental instructions: sin, cos and tangent. From other
new features of the co-processor it's worth to mention more rounding
options - they can be specified on per-instruction basis. The
co-processor also has second set of FPU registers - each instruction
specifies which register set will be used during instruction execution.
The WE32206 co-processor supports two modes of operation:
- Co-processor mode. In this mode the FPU communicates directly with
the main processor. There are 10 co-processor instructions recognized
by CPU - these instructions tell the main processor the types of
co-processor operands and how many operands are required. The
co-processor instructions also contain actual WE32206 instruction
op-codes, which are passed to the FPU. Then, if the FPU needs to read
data from memory, the CPU initiates reading and the FPU fetches data
from the bus. When the FPU completes instruction execution it
automatically notifies the processor, and sends condition codes and
exception data to the CPU. If the FPU needs to write data to memory,
the CPU initiates write operation and the FPU supplies the resulting
data.
- Peripheral mode. In this mode the FPU works as a memory-mapped
device, and the CPU or other device can write directly to FPU
registers by writing to specific memory addresses assigned to the
co-processor. When the FPU completes instruction execution the CPU
can read the contents of FPU registers, condition codes and exception
data by reading memory assigned to the FPU. If necessary, the 32206
can be configured to generate interrupt each time it completes
instruction execution.
The advantages of peripheral mode are:
- The WE32206 can be used with any CPU
- The FPU can execute instructions with three memory operands, while
in co-processor mode is limited to two memory operands.
The disadvantage of peripheral mode is that it's slightly slower than
the co-processor mode.
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