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TEST CAPABILITIES
The TLB lookup operation progresses
as
follows:
• The linear address and tag values are written to the command register,
as
well as a 1
value for bit
O.
• New values for the hit/miss bit and replacement pointer are written to bits 4-2 in the
data register.
If
the hit/miss bit (bit
4)
is
1,
bits 31-12 contain the physical address
from the TLB.
Otherwise, bits 31-12 are undefined.
For more information on how to write routines to test the TLB, refer to the
386™
DX
Microprocessor Programmer's Reference Manual.
12.2 BOARD
..
LEVEL TESTS
For board-level testing, it
is
often desirable to isolate areas of the board from the inter-
actions of other devices. The Inte1386 DX microprocessor can be forced to a state in
which all but two of its pins are effectively removed from their circuits. This state
is
accomplished through the HOLD and HLDA pins.
When the
HOLD input
of
the Inte1386 DX microprocessor
is
asserted, the Intel386
DX
microprocessor places all of its outputs except for HLDA in the three-state condition.
HLDA
is
then driven high. The Intel386
DX
microprocessor remains in this condition
until
HOLD
is
de-asse,rted. Note that RESET being asserted takes priority over
HOLD
requests.
The Inte1386
DX
microprocessor completes its current bus cycle before responding to
the
HOLD input. Detailed information on HOLDIHLDA response
is
given in
Chapter
3.
12-5