
Chapter 5
Signal Descriptions
119
23542A/0—September 2000
AMD-K6-2E+ Embedded Processor Data Sheet
Preliminary Information
5.32
KEN# (Cache Enable)
Pin Attribute
Input
Summary
If KEN# is sampled asserted, it indicates that the address
presented by the processor is cacheable. If KEN# is sampled
asserted and the processor intends to perform a cache-line fill
(signified by the assertion of CACHE#), the processor executes
a 32-byte burst read cycle and expects to sample BRDY#
asserted a total of four times. If KEN# is sampled negated
during a read cycle, a single-transfer cycle is executed and the
processor does not cache the data. For write cycles, CACHE# is
asserted to indicate the current bus cycle is a modified
cache-line writeback. KEN# is ignored during writebacks.
If PCD is asserted during a bus cycle, the processor does not
cache any data read during that cycle, regardless of the state of
KEN#
. See “PCD (Page Cache Disable)” on page 124 for more
details.
If the processor has sampled the state of KEN# during a cycle,
and that cycle is aborted due to the sampling of BOFF#
asserted, the system logic must ensure that KEN# is sampled in
the same state when the processor restarts the aborted cycle.
Sampled
KEN# is sampled on the clock edge on which the first BRDY# or
NA# of a read cycle is sampled asserted. If the read cycle is a
burst, KEN# is ignored during the last three assertions of
BRDY#. KEN# is sampled during read cycles only when
CACHE# is asserted.