Intel 8087 Internal Architecture

Intel 8087 Internal Architecture

The 8087 is divided into 2 sections CU and NEU. That’s is control unit and numeric execution unit.

The numeric execution unit executes all numeric processor instructions while control unit receives, decodes instructions, read and writes memory operands and executes 8087 control instructions.

These 2 units works asynchronously with each other. The control unit is majorly responsible for establishing communication between CPU and memory and also for coordinating internal coprocessor execution.

The NEU has 8 registers 80 bit wide stack that holds operands for arithmetic instructions and their result. The FSTSW AX; is the instructions used for communication between coprocessor and micro processor.

The control unit is used to synchronize operation between coprocessor and microprocessor.  The unit has a control word a status word and a data buffer. If the instruction is an ESCape (coprocessor) instruction the coprocessor executes it otherwise the microprocessor executes it. The status register reflects the overall operation of the coprocessor.

The 8087 is a numeric data processor. It is basically made to work along with the 8086 and 8088 processors. It is incapable of fetching the instructions on its own so it is just simply connected to respective buses of the processor. Its instructions are recognized by word F as each and every instructions starts with F. for example FADD, FSUB etc.

The BUSY pin of the coprocessor is connected to the main processor's TEST pin. This TEST pin is active low in nature. This is because the speed of operation of the coprocessor and the main processor is different.