Western Electric 32106 co-processor

Western Electric 32106 (WE32106) is a Floating Point Unit for WE 32100 microprocessor family. The FPU can execute all basic mathematical operations, comparison and rounding operations, and calculates square root. The WE32106 supports single, double and extended precision floating point numbers. The co-processor can also read and write data in BCD and integer formats. When the 32106 loads the data, it converts it to extended-precision numbers, and all internal operations are performed with these extended-precision numbers.

The WE32106 co-processor has two modes of operation:

• Co-processor mode. In this mode the FPU communicates directly with the 32100 CPU. The CPU recognizes 10 co-processor instructions. These are not instructions for the 32106 FPU - the instructions tell the CPU the types of co-processor operands and how many operands are required. The co-processor instructions also contain actual WE32106 instruction op-code, which is passed to the FPU. Then, if the instruction requires memory data, the CPU starts reading data from memory. This data is ignored by the CPU, but it is fetched by the FPU from the bus. When the FPU completes instruction execution it automatically notifies the CPU, and sends condition codes and exception data to the CPU. If the instruction result should be saved in memory, the CPU initiates write operation, and the FPU supplies the resulting data.
• Peripheral mode. In this mode all FPU registers are mapped in processor memory, and the 32100 or other CPU can write floating-point instructions and data directly to these registers. When the FPU completes instruction execution the CPU can read results, condition codes and exception data from FPU registers.

Peripheral mode of operation is slower than co-processor mode because the CPU has to explicitly write to and read from FPU registers. The advantage of peripheral mode is that it can be used with any CPU. When used with WE32100 CPU, the peripheral mode allows the FPU execute floating-point instructions that work with three memory operands, while in co-processor mode the FPU is limited to two memory operands.