Advertisement
Carry-In From 2
Not Carry-In
Not Al
A
N
OR
Not Bl
0
Output
LM
~
-'/
Not Al
N
Bl
N
D
LM
~
'-----
Al
N
Not Bl
D
N
---;;:-
Al
N
Bl
D
AOll
Not LM
A
Not Al
N
OR
Bl
0
Not Al
,-----
Not LM
~
Not Bl
Al
N
N
-
Not Bl
D
Connect
Not N
~
~
Al
N
Bl
0
AOl2
Table 1
Function
Connect
LM
N
A+B
Off
Off
On
Not Connect
A.,.B
On
Off
On
Al
A and B
On
On
·Off
Bl
A or B
On
Off
Off
Figure 2-28.
ALU l-Bit
If both (or neither) A and B inputs
have bits, AOI 2 will provide the up
level to switch with Carry or No Carry
at AOI 4 or AOI 3 to provide the Sum
1
or not Sum
1
signals.
The above des-
cription of this part of the add opera-
tion also applies to the
E~clusive
Or
function.
The carry or not carry from a bit
position (which will be used in the
creation of the next bit sum) is created
in the following manner:
Assuming a carry in condition (Carry.
In line up and Not Carry In line down)
meatlsthat no inputs can be active to
AOI 5 and that an input must be active
at AOI 6.
The condition at AOI 5 can be
satisfied by a down level from AOI
1
A
OR
N
-
-
D
Sum 1 +L
-;;:-
N
N
-
D
AOl3
A
N
OR
, - -
D
Not Sum 1 +L
~
N
--
N
' - - -
D
AOl4
A
OR
~
N
D
~
, - -
N
Carry 1 +L
D
N
~
' - - -
N
D
AOl5
A
-
OR
N
-
D
Not Carry 1 +L
~
N
N
-
D
AOI 6
(neither or both bits present at input)
or by a carry into the bit one position
(in this case the Not Carry In line will
be down).
The Not Carry
1
line is
brought down through AOI 6 by either the
presence of bits on both A and B or by a
bit on either A or B (up level from AOI
1)
together with a carry in.
For the
Exclusive Or operation, the Connect line
is activated which effectively elimi-
nates the carry circuit by bringing down
the carry
1
line through AOI 5 and
bringing up the Not Carry
1
line through
AOI 6 (all inputs down).
AND Operation
The function is identical to the logical
AND circui t requiring the presence o.f
all inputs in order to create an output
2-17
Advertisement
