Y240~A~OOM202
REV.
-=-
THE SINGER COMPANY
, KEARFOTTDiV1SION
of
the last instruction executed
is
displayed by
the
DATA Indicator lights. The meaningful data
that
can be viewed
in
the display
is
as
follows:
(A)
A .Register (32 bits)
{B) B Register (32 bits)
(X)
Index Register (18 bits)
(PI) Program Interrupt
Mask
Register (16 bits)
(ST)
Status Register (16 bits)
(PC)
Program Counter (18 bits)
Contains
the
contents of the most recently
used index register.
Contains thefoltOwing status information:
the group
of
index registers selected, short
address extension bits, program flags,
interrupt enable, carry and overflow bits,
and
the
halfword arithmetic indicator.
Contains
the
target address of the next
instruction
to
be executed, when computer
has executed instructions from memory.
When
executing instructions from
the
CCU
panel,
this display
is
meaningless.
If,
in
the
skip and transferinstructions
and a condition
is
required without being
met, there
the
PC
contains the final address
plus
1.
For non-conditional transfers, the
PC
always contains the target address.
Not listed above are
the
C and Dregisters, which are intermediate registers, and are'not accessible
to
the
programmer.
In
the case
of
position X, the register displayed
will
depend upon the condition of
status register bits 0 and 1, and on the condition
of
the
Xl
or
X2field
bits
ofthelast
instruction
that
used indexing.
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