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LOCALBU51NTERFACE
Table 3-5. Generation of BHE#, BLE#, and A 1 from Byte Enables
80386 Signals
16-Bit Bus Signals
Comments
BE3#
BE2#
BE1#
BEO#
A1
BHE#
BLE# (AO)
H*
H*
H*
H*
x
x
x
x-no active bytes
H
H
H
L
L
H
L
H
H
L
H
L
L
H
H
H
L
L
L
L
L
H
L
H
H
H
H
L
H*
L*
H*
L*
x
x
x
x-not contiguous bytes
H
L
L
H
L
L
H
H
L
L
L
L
L
L
L
H
H
H
H
L
H
L*
H*
H*
L*
x
x
x
x-not contiguous bytes
L*
H*
L*
H*
x
x
x
x-not contiguous bytes
L *
H*
L*
L*
x
x
x
x-not contiguous bytes
L
L
H
H
H
L
L
L*
L*
H*
L*
x
x
x
x-not contiguous bytes
L
L
L
H
L
L
H
L
L
L
L
L
L
L
BLE# asserted when 00-07 of 16-bit bus is active.
BHE# asserted when 08-015 of 16-bit bus is active.
A1
low for all even words;
A1
high for all odd words.
Key:
x = don't care
H = high voltage level
L = low voltage level
* = a non-occurring pattern of Byte Enables; either none are asserted, or the pattern has Byte Enables
asserted for non-contiguous bytes
Table 3-6. Byte Enables during B516 Cycles
First Cycle:
Second Cycle:
BE3#
BE2#
BE1#
BEO#
BE3#
BE2#
BE1#
BEO#
High
High
High
Low
None
High
High
Low
High
None
High
High
Low
Low
None
High
Low
High
High
None
High
Low
Low
High
High
Low
High
High
High
Low
Low
Low
High
Low
High
High
Low
High
High
High
None
Low
Low
High
High
None
Low
Low
Low
High
Low
Low
. High
High
Low
Low
Low
Low
Low
Low
High
High
3-23
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