Intel 80C188XL, 80C186XL user manual System Design Tips

Models: 80C186XL 80C188XL

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11.4.3 System Design Tips

MATH COPROCESSING

Bus cycles involving the 80C187 Math Coprocessor behave exactly like other I/O bus cycles with respect to the processor’s control pins. See “System Design Tips” for information on integrating the 80C187 into the overall system.

11.4.3 System Design Tips

All 80C187 operations require that bus ready be asserted. The simplest way to return the ready indication is through hardware connected to the processor’s external ready pin. If you program a chip-select to cover the math coprocessor port addresses, its ready programming is in force and can provide bus ready for coprocessor accesses. The user must verify that there are no conflicts from other hardware connected to that chip-select pin.

A chip-select pin goes active on 80C187 accesses if you program it for a range including the math coprocessor I/O ports. The converse is not true — a non-80C187 access cannot activate N CS (nu- merics coprocessor select), regardless of programming.

In a buffered system, it is customary to place the 80C187 on the local bus. Since DTR and DEN function normally during 80C187 transfers, you must qualify DEN with NCS (see Figure 11-3). Otherwise, contention between the 80C187 and the transceivers occurs on read cycles to the 80C187.

The microprocessor’s local bus is available to the integrated peripherals during numerics execu- tion whenever the CPU is not communicating with the 80C187. The idle bus allows the processor to intersperse DRAM refresh cycles and DMA cycles with accesses to the 80C187.

The microprocessor’s local bus is available to alternate bus masters during execution of numerics instructions when the CPU does not need it. Bus cycles driven by alternate masters (via the HOLD/HLDA protocol) can suspend coprocessor bus cycles for an indefinite period.

The programmer can lock 80C187 instructions. The CPU asserts the LOCK pin for the entire du- ration of a numerics instruction, monopolizing the bus for a very long time.

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Intel 80C188XL, 80C186XL user manual System Design Tips