8086
Table 1. Pin Description (Continued)
Name and Function
Symbol
QS , QS
Pin No.
24, 25
Type
O
QUEUE STATUS: The queue status is valid during the CLK cycle after
which the queue operation is performed.
QS and QS provide status to allow external tracking of the internal
1
0
1
0
8086 instruction queue.
QS
QS
Characteristics
No Operation
1
0
0 (LOW)
0
0
1
0
1
First Byte of Op Code from Queue
Empty the Queue
Subsequent Byte from Queue
1 (HIGH)
1
e
functions which are unique to minimum mode are described; all other pin functions are as described above.
The following pin function descriptions are for the 8086 in minimum mode (i.e., MN/MX
V
). Only the pin
CC
M/IO
28
29
O
O
STATUS LINE: logically equivalent to S in the maximum mode. It is used to
2
distinguish a memory access from an I/O access. M/IO becomes valid in
the T preceding a bus cycle and remains valid until the final T of the cycle
4
4
LOW). M/IO floats to 3-state OFF in local bus ‘‘hold
e
acknowledge’’.
e
(M
HIGH, IO
WR
WRITE: indicates that the processor is performing a write memory or write
I/O cycle, depending on the state of the M/IO signal. WR is active for T , T
and T of any write cycle. It is active LOW, and floats to 3-state OFF in
2
3
W
local bus ‘‘hold acknowledge’’.
INTA
ALE
24
25
O
O
INTA: is used as a read strobe for interrupt acknowledge cycles. It is active
LOW during T , T and T of each interrupt acknowledge cycle.
2
3
W
ADDRESS LATCH ENABLE: provided by the processor to latch the
address into the 8282/8283 address latch. It is a HIGH pulse active during
T
1
of any bus cycle. Note that ALE is never floated.
DT/R
27
26
O
O
DATA TRANSMIT/RECEIVE: needed in minimum system that desires to
use an 8286/8287 data bus transceiver. It is used to control the direction of
data flow through the transceiver. Logically DT/R is equivalent to S in the
1
e
e
LOW.) This signal floats to 3-state OFF in local bus ‘‘hold acknowledge’’.
maximum mode, and its timing is the same as for M/IO. (T
HIGH, R
DEN
DATA ENABLE: provided as an output enable for the 8286/8287 in a
minimum system which uses the transceiver. DEN is active LOW during
each memory and I/O access and for INTA cycles. For a read or INTA cycle
it is active from the middle of T until the middle of T , while for a write cycle
2
4
it is active from the beginning of T until the middle of T . DEN floats to 3-
2
state OFF in local bus ‘‘hold acknowledge’’.
4
HOLD,
HLDA
31, 30
I/O
HOLD: indicates that another master is requesting a local bus ‘‘hold.’’ To be
acknowledged, HOLD must be active HIGH. The processor receiving the
‘‘hold’’ request will issue HLDA (HIGH) as an acknowledgement in the
middle of a T or T clock cycle. Simultaneous with the issuance of HLDA
i
4
the processor will float the local bus and control lines. After HOLD is
detected as being LOW, the processor will LOWer the HLDA, and when the
processor needs to run another cycle, it will again drive the local bus and
control lines. Hold acknowledge (HLDA) and HOLD have internal pull-up
resistors.
The same rules as for RQ/GT apply regarding when the local bus will be
released.
HOLD is not an asynchronous input. External synchronization should be
provided if the system cannot otherwise guarantee the setup time.
5
INTEL [ INTEL ]
