AMD AMD5K86 - TABLE 5-12. Outputs Floated When HLDA Is Asserted; HLDA (Bus-Hold Acknowledge)

18524B/O-Mar1996
Signal Descriptions
AMDl'
AMD5~6 Processor Technical Reference Manual
The processor drives writebacks by asserting ADS and either
reusing the inquire cycle address (if AHOLD is held asserted
throughout the writeback) or driving the address itself (if
AHOLD is
negated for the write back, or if BUFF or HOLD was
used to obtain the bus). If AHOLD is held asserted throughout
an inquire cycle and a subsequent writeback, system logic
must latch the inquire cycle address when it asserts EAIJS and
use the latched copy during the writeback. By contrast, if sys-
tem logic always negates AHOLD before the write back, the
processor drives the writeback address when it asserts ADS for
the writeback, and system logic need not latch a copy of the
inquire cycle address.
Inquire cycles can be driven while LOCK is asserted, if
AHOLD is used to obtain the bus for the inquire cycle. An
inquire cycle cannot hit a line involved in a locked operation.
Cached locations that are about to be accessed in locked opera-
tions are written back and invalidated before the locked opera-
tion occurs. If such an inquire cycle hits a modified location
that is different than the one involved in the locked operation,
the write back is done in the middle of the locked operation,
between the two locked cycles, and LOCK is asserted during
the writeback. This is the only case in which another operation
can intervene in a locked operation. System logic must recog-
nize this case and know that the inquire cycle is snooping a dif-
ferent location than the one that is locked.
At the falling edge of RESET, the states of BRDYC and BUs:
CHK control the drive strength on the A21-A3 (not including
A31-A22), ADS, HITlVI, and WIR signals. The drive strength is
weak for all states of BRDYC and BUSCHK except when
BRDYC and BUSCHK are both Low, in which case the drive
strength is strong. The A31-A22 signals use the weak drive
strength at all times. See the data sheet for details.
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