8088
Table 1 Pin Description
(Continued)
Symbol Pin No
HOLD
31 30
HLDA
Type
Name and Function
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 T4 or
Ti clock cycle Simultaneous with the issuance of HLDA the processor will float
the local bus and control lines After HOLD is detected as being LOW the
processor lowers HLDA and when the processor needs to run another cycle it
will again drive the local bus and control lines HOLD and HLDA have internal
pull-up resistors
Hold is not an asynchronous input External synchronization should be provided if
the system cannot otherwise guarantee the set up time
O
STATUS LINE
is logically equivalent to SO in the maximum mode The
combination of SSO IO M and DT R allows the system to completely decode the
current bus cycle status
IO M
1(HIGH)
1
1
1
0(LOW)
0
0
0
DT R
0
0
1
1
0
0
1
1
SSO
0
1
0
1
0
1
0
1
Characteristics
Interrupt Acknowledge
Read I O Port
Write I O Port
Halt
Code Access
Read Memory
Write Memory
Passive
SSO
34
The following pin function descriptions are for the 8088 8288 system in maximum mode (i e MN MX
e
GND) Only the pin functions which are unique to maximum mode are described all other pin functions are as
described above
Symbol Pin No Type
Name and Function
S2 S1 S0 26– 28
O
STATUS
is active during clock high of T4 T1 and T2 and is returned to the
passive state (1 1 1) during T3 or during Tw 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 S2 S1 or S0 during T4 is used to indicate the beginning
of a bus cycle and the return to the passive state in T3 and Tw is used to
indicate the end of a bus cycle
These signals float to 3-state OFF during ‘‘hold acknowledge’’ During the first
clock cycle after RESET becomes active these signals are active HIGH After
this first clock they float to 3-state OFF
S2
S1
S0
Characteristics
0(LOW)
0
0
Interrupt Acknowledge
0
0
1
Read I O Port
0
1
0
Write I O Port
0
1
1
Halt
1(HIGH)
0
0
Code Access
1
0
1
Read Memory
1
1
0
Write Memory
1
1
1
Passive
4
INTEL [ INTEL CORPORATION ]
