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18522F/0—Jan1997 AMD-K5 Processor Data Sheet

PRELIMINARY INFORMATION

the drive strength is strong. The A31–A22 signals use the weak

drive strength at all times.

BREQ Bus Request Pending Output

The processor asserts the BREQ signal to indicate a request for

the bus. This signal is driven even when the processor floats

the bus (except in Test mode). (See FLUSH.)

BUSCHK Bus Check Input

The BUSCHK signal allows the external system to indicate bus

cycle errors. This signal, when asserted, latchs the address bus.

The control signals in the machine check registers will also

latch. If the MCE bit in CR4 is set, the processor will vector to

the machine check exception at the end of the bus cycle. At the

falling edge of RESET, the states of BRDYC and BUSCHK con-

trol the drive strength on the A21–A3 (not including A31–A22),

ADS, HITM, and W/R signals. The drive strength is weak for all

states of BRDYC and BUSCHK except BRDYC and BUSCHK

both Low, in which case drive strength is strong. A31–A22 use

the weak drive strength at all times.

CACHE Cache Status Output

The CACHE signal is asserted for cacheable read cycles or

burst writeback cycles. A burst access is always four 64-bit

transfers associated with a line refill or a cache write back.

Read data will not be cached if CACHE is negated during a

read cycle, or if KEN is negated. KEN must be asserted during

the first access of a burst transfer. If KEN is negated, a single

access occurs.

CLK Clock Input

The CLK signal is the bus clock for the processor, and is the

primary reference for all bus cycle timings (except for test sig-

nals). It is used with the BF signal to determine the internal

operating speed of the processor. The processor multiplies the

clock input by 1.5 or 2. (See BF.)

D/C Data/Code Output

The D/C signal, driven active with ADS, is used with other con-

trol signals to determine bus cycle and special cycle types. It is

floated with BOFF and bus hold. These cycles are defined in

Table 5 and Table 6 on page 27.

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AMD K5 Manual do Utilizador Página 27