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ClK
BE3#-BEO#
A31-A2
lOCK#
NAn
READY"
LOCAL BUS INTERFACE
UNLOCKED
lOCKED
lOCKED
UNLOCKED
BUS CYCLE
BUS CYCLE BUS CYCLE
BUS CYCLE
Figure 3-20. LOCK# Signal during Address Pipelining
G30107
and the 80386 performs a LOCKed read of the gate in the IDT (8 bytes), a read of the
target descriptor (8 bytes), and a write of the accessed bit in the target descriptor.
3.6
HOLD/HLDA (Hold Acknowledge)
The 80386 provides on-chip arbitration logic that supports a protocol for transferring control
of the local bus to other bus masters. This protocol is implemented through the HOLD input
and HLDA output.
3.6.1 HOLD/HLDA Timing
To gain control of the local bus, the requesting bus master drives the 80386 HOLD input
active. This signal must be synchronous to the CLK2 input of the 80386. The 80386 responds
by completing its current bus cycle (plus a second locked cycle or a second cycle required
by BS16#). Then the 80386 sets all outputs but HLDA to the three-state OFF condition to
effectively remove itself from the bus and drives HLDA active to signal the requesting bus
master that it may take control of the bus.
3-34
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