Intel 80386

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
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