Intel 8086-1 - Manual (Page 3)

8086
Table 1 Pin Description (Continued)
Symbol Pin No Type Name and Function
READY 22 I READY is the acknowledgement from the addressed memory or I O
device that it will complete the data transfer The READY signal from
memory IO is synchronized by the 8284A Clock Generator to form
READY This signal is active HIGH The 8086 READY input is not
synchronized Correct operation is not guaranteed if the setup and hold
times are not met
INTR 18 I INTERRUPT REQUEST is a level triggered input which is sampled
during the last clock cycle of each instruction to determine if the
processor should enter into an interrupt acknowledge operation A
subroutine is vectored to via an interrupt vector lookup table located in
system memory It can be internally masked by software resetting the
interrupt enable bit INTR is internally synchronized This signal is
active HIGH
TEST 23 I TEST input is examined by the ‘‘Wait’’ instruction If the TEST input is
LOW execution continues otherwise the processor waits in an ‘‘Idle’’
state This input is synchronized internally during each clock cycle on
the leading edge of CLK
NMI 17 I NON-MASKABLE INTERRUPT an edge triggered input which causes
a type 2 interrupt A subroutine is vectored to via an interrupt vector
lookup table located in system memory NMI is not maskable internally
by software A transition from LOW to HIGH initiates the interrupt at the
end of the current instruction This input is internally synchronized
RESET 21 I RESET causes the processor to immediately terminate its present
activity The signal must be active HIGH for at least four clock cycles It
restarts execution as described in the Instruction Set description when
RESET returns LOW RESET is internally synchronized
CLK 19 I CLOCK provides the basic timing for the processor and bus controller
It is asymmetric with a 33% duty cycle to provide optimized internal
timing
V
CC
40 V
CC a 5V power supply pin
GND 1 20 GROUND
MN MX 33 I MINIMUM MAXIMUM indicates what mode the processor is to
operate in The two modes are discussed in the following sections
The following pin function descriptions are for the 8086 8288 system in maximum mode (i e MN MX e V
SS
)
Only the pin functions which are unique to maximum mode are described all other pin functions are as
described above
S
2
S
1
S
0
26 – 28 O STATUS active during T
4
T
1
and T
2
and is returned to the passive state
(1 1 1) during T
3
or during T
W
when READY is HIGH This status is used
by the 8288 Bus Controller to generate all memory and I O access control
signals Any change by S
2
S
1
or S
0
during T
4
is used to indicate the
beginning of a bus cycle and the return to the passive state in T
3
or T
W
is
used to indicate the end of a bus cycle
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