IBM 1620 1 Manual page 65

Bypass. The Bypass light shows that the
MAR
address
neither decreased nor increased. When this light is
on, either the Increment or Decrement light is also on.
DECR (Decrement). The Decrement light shows that
the address routed from
MAR
to
MARS
decreases by 1,
unless the Bypass light is also on. Both lights, when
on, indicate that no decrease occurred.
INCR (Increment). The Increment light shows that
the address routed from
MAR
to
MARS
increases by 1,
unless the Bypass light is also on. Both lights, when
on, indicate that no increase occurred.
Plus 2. The Plus 2 light shows that the address routed
from
MAR
to
MARS
increases by 2. When this light is
on, the Increment light must also be on.
Branch. The Branch light comes on during the I cycle
of Branch Indicator and Branch No Indicator instruc-
tions if the branch is to occur during the E cycle.
RECOA1P (Recomplement). The Recomplement light
shows that an add or subtract result will be recom-
plemented upon completion of the computation.
Carry Out. The Carry Out light shows that the result
from the Add table has a carry (flag bit) or that a
carry was placed into a position containing a nine,
which causes the Carry Out light to come on one to
three storage cycles later.
Carry In. The Carry In light is turned on by a carry
out and shows that 1 will be added on the next ma-
chine cycle.
I/ A (Indirect Addressing). The Indirect Addressing
light shows that an indirect addressing operation (spe-
cial feature) is in process. It is turned on when a flag
bit is present in the units position of the indirect ad-
dress.
Field Mk 1 (Field Mark 1). The Field Mark 1 light
comes on when the flag bit in the high-order position
of the
Q
field is detected in the
MDR.
Field Mk 2 (Field Mark 2). The Field Mark 2 light
comes on when the flag bit in the high-order position
of the P field is detected in the
MDR.
COMP (Complement). When the Complement light
is on, it shows that the Q address data is comple-
mented during arithmetic operations.
Mask. (1710 Control System only). The Mask light
is turned on by the execution of a Mask instruction,
and is turned off by the execution of an Unmask in-
struction. This light is also turned on when the 1620
Reset key is pressed, or by a Power-on operation.
Interrupt Mode. (1710 Control System only.) The
Interrupt Mode light is turned on only when an inter-
rupt is recognized. It is on while the interrupt is being
serviced, and is turned off by the execution of a
Branch Out of Noninterruptible :Mode or a Branch
Out of Noninterruptible Mode and Load instruction.
In effect, the Interrupt Mode light is on when IR-3
is used in place of IR-l.
Instruction and Execute Cycle Lights
The Instruction and Execute Cycle lights (Figure 56)
are visual aids for the console operator in stepping
an instruction through I and E cycles with the Instant
Stop/seE key. The I and E lights progress through
each cycle with repeated depressions of this key.
Input/Output Lights
The Input/Output lights are primarily used by
IBM
Customer Engineers for diagnostic testing.
LC (Last Card). The Last Card light has significance
for the operator and programmer. This light turns on
when data from the last card has been transferred
from 1622 input buffer storage to 1620 core storage
without a parity error.
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