Intel 386 manual Local BUS Activity with the Intel387 OX Math Coprocessor, CLK2

COPROCESSOR HARDWARE INTERFACE

•In pseudo-synchronous mode, CKM is low and a frequency source for the 387CLK2 input must be provided. Only the interface logic of the Intel387 DX math coprocessor is synchronous with the Inte1386 DX microprocessor. The internal logic of the Intel387 DX math coprocessor operates from the 387CLK2 clock source, whose fre- quency may be 10/16 to 14/10 times the speed of CLK2. Figure 5-2 depicts pseudo- synchronous operation.

5.2LOCAL BUS ACTIVITY WITH THE Intel387 OX MATH COPROCESSOR

The Inte1387 DX math coprocessor uses two distinct methods ,to interact with the Intel386 DX microprocessor:

•The Inte1386 DX microprocessor initiates coprocessor operations during the execu- tion of a coprocessor instruction (an ESC instruction). These interactions occur under program control.

•The coprocessor uses the PEREQ signal to request the Inte1386 DX microprocessor to initiate operand transfers to or from system memory. These operand transfers occur when the Intel387 DX math coprocessor requests them; thus, they are asyn- chronous to the instruction execution of the Intel386 DX microprocessor.

When the Inte1386 DX microprocessor executes an ESC instruction that requires trans- fers of operands to or from the coprocessor, the Intel386 DX microprocessor automati- cally sets an internal memory address base register, memory address limit register, and' direction flag. The (;oprocessor can then request operand transfers by driving PEREQ active. These requests occur only when the coprocessor is executing an instruction (when BUSY# is active).

CLK2 -		INTERFACE	SYNCHRONOUS
		.NUMERIC	ASYNCHRONOUS
		CORE
i386~	ox CPu	i387'·ox
		MATH

387CLK2 COPROCESSOR

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Figure 5-2.Pseudo-Synchronous Interface

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