Data And Instruction Format; Data Formats; Unpacked Format; Edited Format - RCA Spectra 70 Training Manual

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DATA AND INSTRUCTION FORMAT
DATA FORMATS
When representing data, a byte may store a single
character (unpacked format), or two numeric digits
(packed format).
UNPACKED FORMAT
A byte in the unpacked format uses all eight bits to
represent one alphabetic or numeric character. This
format, for example is required for the storage of
any characters that are to appear on any type of dis-
play output such as the Printer or Typewriter.
Some of the more commonly used characters, and
the hexadecimal representation of their bytes are as
indicated in the tables below.
ALPHABETIC
NUMERIC
Char. Hex. Char. Hex. Char. Hex. Char. Hex.
0
FO
A
Cl
J
Dl
1
Fl
B
C2
K
D2
S
E2
2
F2
C
C3
L
D3
T
E3
3
F3
D
C4
M
D4
U
E4
4
F4
E
C5
N
D5
V
E5
5
F5
F
C6
0
D6
W
E6
6
F6
G
C7
P
D7
X
E7
7
F7
H
C8
Q
D8
y
E8
8
F8
I
C9
R
D9
Z
E9
9
F9
SPECIAL CHARACTERS
Char.
Hex.
Char.
Hex.
BLANK
EO
- (Minus
60
. (Period)
4B
/
Hyphen)
61
<
4C
, (Comma)
6B
(
4D
%
6C
+
4E
#
7B
&
50
@
7C
$
5B
t
(Quote)
7D
*
5C
=
7E
)
5D
Space
40
A decimal numeric field in unpacked format is
assumed to contain a sign in the high-order four bits
of the right most byte. All other bytes, in the zone
portion, will have the four high-order bits a value of
all ones (1111 2 ),
However, the decimal numeric field must be packed
before it may be used as an operand in a decimal
arithmetic operation.
6
PACKED DATA FORMAT
In packed data format, one byte stores two decimal
digits except for the rightmost byte which contains the
sign in the four low-order bits.
The following example shows the same field in un-
packed and packed format. Each location represents
a byte shown in hexadecimal format.
UNPACKED
PACKED
1
FO
1
F3
1
F1
I
F6
1
F2
1
F1
I
80
I
103
I
16
1
21
1
OS
I
It should be noted (as in the example above) that when
either packing or unpacking a field the rightmo st byte
has its zone and numeric portions reversed.
SIGN RECOGNITION
In decimal arithmetic operations the sign of a field
is recognized as positive ifthe sign position contains:
(1)
All one bits (1111)2
(2)
Qriftherightmostbitisa(0}z Le., (1010)2'
(1110)2'
If
the sign has a low-order bit of (1) 2' and at least
one of the remaining bits is (0) 2' it is considered
negative.
Mter a decimal arithmetic operation the sign of the
result is one of the following:
(1100)2 for positive
(1101)2 for negative
Thus, in preparing source card input for numeric
data fields, the user may follow existing procedures,
L e., for a negative field an overpunch of the minus
(11 punch) in the least significant position generates
a zone portion of (1101 2 ),
EDITED FORMAT
A packed numeric field may be placed in edited
format with a single EDIT instruction (see page 33).
A field in edited form is unpacked and contains neces-
sary edit symbols.
01
01
I
23
48
+
I -
1 -
1
0
1
1
2
3
4
1 -I

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