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Spare
1st Character
2nd Character
0
0
C
D
D
P
D
D
D
D
C
D
D
P
D
D
D
D
18
17
16
9
8
1
Two 8-level characters still containing parity and control bits, where:
C
Control Bit
D
Data Bit
P
Parity Bit
Numeric Data
Positive numbers are represented by integers.
Negative numbers are represented in the 2's
complement form.
The DATANET-30 utilizes 2's complement arithmetic. Therefore, the
high-order bit is properly thought of as the sign bit, when it is understood that the sign is a
2' s complement sign, not an algebraic sign.
The bits are shown in groups merely to simplify
the presentation.
There is no hardware sign bit in either the A or B registers. The sign is
always programmed.
- - - - - - - - - - T h e Sign (in the two's
complement sense)
- - - - - - - - - T h e Number
1]
The number is considered a 1 7-bit number with bit 18 as the sign bit. In case of overflow
of a positive number into bit 18 position, the sign changes and goes negative. Conversely, with
a negative number, bit 18 will change in the event of overflow. This condition is tested with
a Branch On Plus dr Branch On Minus instruction.
IDJ&u&~~uc:J ~@------------
I-27
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