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SECTION II.
OPERATOR'S CONTROL PANEL
the RESET DC OFF button.
If the RUN button has been depressed, the
RESET DC OFF switch is not effective until the STOP button is depressed.
The RESET DC OFF indicator is illuminated by the power checks (see
page 2-12) and is turned off when the DC ON switch is depressed.
When
the RESET DC OFF button is illuminated by a VOLTAGE check, it.
glows red; in other cases it is white.
Following a VOLTAGE check,
depressing the RESET DC OFF button resets only the VOLTAGE check
indicator.
The RESET DC OFF switch has no affect on a-c power •
ADDRESS MODE Buttons
•
ADDRESS
m
Two separate illuminating ADDRESS MODE push buttons labelled "2" and "3" are provided
on the control panel.
The "2" button is illuminated when the central processor is in the two-
character addressing mode (specifying anyone of 4,096 locations).
The "3" button is illuminated
when in the three-character mode (specifying anyone of 32,768 memory locations plus address
modification information).
The appropriate button is illuminated from instant to instant as the
central processor changes addressing modes.
The push buttons are effective only when the
system is in the STOP mode.
However, when the INITIALIZE button is pressed, the two-char-
acter mode without item-mark trapping is entered regardless of the previous mode.
INTERRUPT Push-Button Indicator
The Type 121 Central Processor control panel is equipped with an INTERRUPT push button
indicator.
The INTERRUPT button is effective at all times, even when the system is in the
STOP mode.
If the INTERRUPT button is pressed while the system is in the STOP mode, the
control panel interrupt demand is set, but the INTERRUPT indicator is not illuminated until the
system subsequently enters the RUN mode (as a result of pressing the RUN button) and the
interrupt signal is actually honored.
For an interrupt signal to be honored, the following conditions must be satisfied:
1.
The central processor is in the RUN mode;
2.
The central processor is not already in the external interrupt mode;
3.
The central processor is about to extract the op code of an instruction; and
4.
A memory cycle is allocated to the central processor.
If the external interrupt demand is set and the above conditions are satisfied, the central
processor enters the external interrupt mode and the INTERRUPT indicator becomes illuminated
and remains so as long as the central processor is in the external interrupt mode.
In addition,
as the external interrupt mode is entered, the EXTERNAL indicator in the lower right corner of
the control panel (see page 2-12) is illuminated and remains so for the duration of the interrupt.
2-10
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