IBM 7090 Instruction-Reference page 148

Divide Check
The divide check lamp is turned on in fixed point division if the dividend accumu-
lator (AC) is greater than or equal to the divisor (storage register). In floating-
point divide the lamp is on if the magnitude of the fraction of the dividend is greater
than or equal to twice the magnitude of the fraction of the divisor. The indicator may
be tested by the DCT instruction .•
Channel Select (A-H)
The channel select (A-H) lamps, one for each channel, are on according to the
data channel that is in operation. They are off when the channel is not in operation.
Command Word Trap (Channels A-H)
These lamps are turned on according to the corresponding channel that is enabled
to trap on command word or end of file. The lamp for a particular channel is turned
off when the channel is disabled.
Tape Check Trap (Channels A-H)
These lamps are on according to the corresponding channel that is enabled to trap
on a tape check. The lamp for a particular channel is off when the channel is disabled.
Channel Tape Check
These lamps, one for each channel, are on if any error is detected while writing
or reading. The lights may be turned off by the execution of a Transfer on Redundancy
Check instruction.
Trap Control
This lamp is on when the channel is not executing a channel trap.
It
is off when
any channel enters a trap condition. While the light is off, no channel traps may be
executed. Channel traps may be executed only when the light is on at the same
time as any of the enabled lamps.
Program Stop (Red)
The program stop lamp is turned on whenever the computer executes a halt instruc-
tion and no data channels are in operation (DVH or VDH excepted).
1-0 Check (White)
The 1-0 check lamp may be turned on by any of the following conditions:
1.
If aRCH or LCH is decoded and the specified data channel has
not been selected.
2. If, when writing, a data channel data register has not been
loaded with a word from storage by the time its contents are
to be sent to the output unit.
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