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urn on
A
A-I
-
Time T4
-
A-2
"""-
01
CD
r--
Turn on B
~
CD
r -
Reset
N
~
A-3
' - -
~
r-
eD
Latch Back
(j)
T4 and Turn on A or B turns latch on.
T urn on of latch sends Latch Back
pulse to switch with (not) Reset to
keep latch on.
Reset deconditions A-3 to turn latch
off.
Figure 2-35.
One Latch Position
of a Register
Latch on
The second type of latch used for
registers is one which is made of sever-
al block functions tied together.
They
can be called AOI latches as they use
AND fUnctions and OR inverter fUnctions.
A latch back line from the output
01
keeps the latch on, as shown in Figure
2-35.
The latch can have many turn-on
lines and will stay turned on until
reset.
This allows greater flexibility,
as the output lines can be tested and
switched with other conditions to con-
trol operations several cycles later.
This AOI latch is used for:
1.
the F-register
2.
the S-register
3.
the control register
4.
the machine check register
REVIEW QUESTIONS - REGISTERS
1.
Registers are used as
latches.
2.
Registers are controlled by
3.
The two types of hard'Nare used for
latches are
latch-
es and
latches.
4.
Register read out is
non-destructive.
(True/False)
5.
All registers read out to the B-bus
but only three registers read out to
the A-bus.
(True/False)
CORE STORAGE
ADDRESSING THEORY
Four-Digit Addressinq
•
•
•
A storage location is a place 'Nhere
something may be kept.
A number assigned to a storage loca-
tion is its storage address.
Four binary digits form 16 different
storage addresses.
By definition a storage location is a
place where something may be kept.
Examples of storage locations are
shelves in a library or mail boxes.
To
facilitate finding things at different
storage locations, it is convenient to
assign a number to each storage
location.
These numbers become the
storage addresses.
USing four binary digits, 16 storage
locations can be assigned addresses.
All items numbered 0000 (decimal 00)
that we wish to store are placed in
storage location 0000 (decimal 00); all
items numbered 0001 (decimal 01) that we
'Nish to store are placed in
storag~
location 0001 (decimal 01); etc.
It is
now possible to find any item by select-
ing the storage location 'Nith the proper
number.
In Figure 2-36 storage location
0101 (decimal 05) has been selected by
the combination of binary digits that
represent the decimal number 05.
2-23
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