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80C186EB/80C188EB, 80L186EB/80L188EB
Table 3. Pin Descriptions
(Continued)
Pin
Pin
Input
Output
Description
Name
Type
Type
States
A18:16
I/O
A(L)
H(Z)
These pins provide multiplexed
Address
during the address
phase of the bus cycle. Address bits 16 through 19 are presented
A19/ONCE
R(WH)
on these pins and can be latched using ALE. These pins are
(A15:A8)
P(X)
driven to a logic 0 during the data phase of the bus cycle. On the
(A18:16)
80C188EB, A15 – A8 provide valid address information for the
(A19/ONCE)
entire bus cycle. During a processor reset (RESIN active), A19/
ONCE is used to enable ONCE mode. A18:16 must not be driven
low during reset or improper operation may result.
S2:0
O
Ð
H(Z)
Bus cycle
Status
are encoded on these pins to provide bus
transaction information. S2:0 are encoded as follows:
R(Z)
P(1)
S2
S1
S0
Bus Cycle Initiated
0
0
0
Interrupt Acknowledge
0
0
1
Read I/O
0
1
0
Write I/O
0
1
1
Processor HALT
1
0
0
Queue Instruction Fetch
1
0
1
Read Memory
1
1
0
Write Memory
1
1
1
Passive (no bus activity)
ALE
O
Ð
H(0)
Address Latch Enable
output is used to strobe address
information into a transparent type latch during the address phase
R(0)
of the bus cycle.
P(0)
BHE
O
Ð
H(Z)
Byte High Enable
output to indicate that the bus cycle in progress
is transferring data over the upper half of the data bus. BHE and
(RFSH)
R(Z)
A0 have the following logical encoding
P(X)
A0
BHE
Encoding
(for the 80C186EB/80L186EB only)
0
0
Word Transfer
0
1
Even Byte Transfer
1
0
Odd Byte Transfer
1
1
Refresh Operation
On the 80C188EB/80L188EB, RFSH is asserted low to indicate a
refresh bus cycle.
RD
O
Ð
H(Z)
ReaD
output signals that the accessed memory or I/O device
must drive data information onto the data bus.
R(Z)
P(1)
WR
O
Ð
H(Z)
WRite
output signals that data available on the data bus are to be
written into the accessed memory or I/O device.
R(Z)
P(1)
READY
I
A(L)
Ð
READY
input to signal the completion of a bus cycle. READY
must be active to terminate any bus cycle, unless it is ignored by
S(L)
correctly programming the Chip-Select Unit.
DEN
O
Ð
H(Z)
Data ENable
output to control the enable of bi-directional
transceivers in a buffered system. DEN is active only when data is
R(Z)
to be transferred on the bus.
P(1)
NOTE:
Pin names in parentheses apply to the 80C188EB/80L188EB.
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