M80287

The M80287 Numeric Processor Extension (NPX) provides arithmetic instructions for a variety of numeric data types in M80286/20 systems. It also executes numerous built-in transcendental functions (e.g., tangent and log functions). The M80287 executes instructions in parallel with an M80286. It effectively extends the register and instruction set of
an M80286/10 system for existing M80286 data types and adds several new data types as well. Figure 3 presents the program visible register model of the M80286/20. Essentially, the M80287 can be treated as an additional resource or an extension to the M80286/10 that can be used as a single unified system, the M80286/20.

The M80287 has two operating modes similar to the two modes of the M80286. when reset, M80287 is in the real address mode. It can be placed in the protected virtual address mode by executing the SETPM ESC instruction. The M80287 cannot be switched back to the real address mode except by reset. In the real address mode, the M80286/20 is completely software compatible with M8086, 88/20.

Once in protected mode, all references to memory for numerics data or status information, obey the M80286 memory management and protection rules giving a fully protected extension of the M80286 CPU. In the protected mode, M80286/20 numerics software is also completely compatible with M8086/20 and M8088/20.

The M80287 has two operating modes similar to the two modes of the M80286. When reset, M80287 is in the real address mode. It can be placed in the protected virtual address mode by executing the SETPM ESC instruction. The M80287 cannot be switched back to the real address mode except by reset. In the real address mode, the M80286/M80287 is completely software compatible with M8086/M8087 and M8088/M8087.

Once in protected mode, all references to memory for numerics data or status information, obey the M80286 memory management and protection rules giving a fully protected extension of the M80286 CPU. In the protected mode, M80286/M80287 numerics software is also completely compatible with M8086/M8087 and M8088/M8087.