8088
Table 1. Pin Description (Continued)
Symbol Pin No. Type
Name and Function
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 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.
SSO
34
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
DT/R
SSO
Characteristics
1(HIGH)
1
1
1
0(LOW)
0
0
0
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Interrupt Acknowledge
Read I/O Port
Write I/O Port
Halt
Code Access
Read Memory
Write Memory
Passive
e
The following pin function descriptions are for the 8088/8288 system in maximum mode (i.e., MN/MX
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
S2, S1, S0 26–28
Name and Function
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
0
1(HIGH)
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Interrupt Acknowledge
Read I/O Port
Write I/O Port
Halt
Code Access
Read Memory
Write Memory
Passive
4
INTEL [ INTEL ]
