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'1'0
review briefly the control of ALU
which is decoded from the CC field of
ROS, the three-column field can-contain
a binary zero through seven, depending
on the punches in the sense card. Fig-
ure 2-26 shows a breakdown of this
punching and of the use of the decoded
mnemonics.· In addition, Figure 2-21
shows that three control lines can be
obtained from various combinations of
mnemonics and that a further decoding
will develop definite functions which
will control the operation of ALU
(Figure 2-28).
Line
CC
.Possible
Nome
Field
Decodes
- -
- - -
{ Not CC2
+L Control LM
Not CCO
010
CC1
i
Not CC1
XOX
+L Control N
Or
' 1
cco
1XX
{ Not CCO}
01X
+L Connect
or
CC1
{
CC1 }
CC2
XII
Figure 2-27.
Decode of ALU
Control Lines
2-16
Numeric
Decode
Mnemonic
2
0
0
1
1
4
DC
5
1C
4
DC
5
1C
6
CC
7
l.f
{
~
Q
{
~
Q
l.f
Add Operation (also Exclusive Or)
From table 1, in Figure 2-28, it can be
seen that control N is the·only control
line activated for A
+
B.
Thus, lines
N, LM will be up and lines N, LM and
Connect will be down during add.
With
these controls, AOI 1 will accept an
input (and its output will be down) if
neither A nor B inputs have a bit or if
both A and B inputs have bits.
The
output of AOI 2 will be down under the
other twb conditions, a bit on A only or
a bit on B only.
Assuming a bit on A
only (or B) the output of AOI 1 will be
up.
This condition will switch with a
carry at AOI 3 or a no carry at ACI 4 to
provide a Sum not 1 or a Sum 1, respec-
tively.
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