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wait state occurs when:
1. The processor-controller is in load or display mode.
2. The processor-controller has been halted by a wait
instruction from the program.
3. STOP or IMMED STOP has been pressed.
The Run Light
being on indicates that the processor-
controller is operating under program control.
The Alarm Light
being on indicates that the operations
monitor has timed out. The alarm light remains on until
the operations monitor switch is turned off. The customer
may install an audible alarm to operate in conjunction with
the alarm light.
Emergency Pull Switch
is for emergency use only. If
pulled out, all electrical power within the processor-
controller is turned off, including power to the blowers
that cool the electronic circuitry. Repeatedly turning the
blowers off in this manner may damage some of the
circuitry. Therefore, use this switch only in emergencies.
The switch must be reset by a customer engineer.
PUSHBUTTON SWITCHES, BOTTOM ROW
(Figure 3)
The Console Interrupt Switch
enables the operator to signal
the program by causing an interrupt. Normally, the
program and sense switches are used in conjunction with
console interrupt to allow operator communication to
the program.
The Load I (Instruction) Switch
is used with the mode
switch positioned at LOAD to transfer the contents of the
data entry switches into the I-register. The processor-
controller is in the stopped condition when it terminates
the load I operation.
The Reset Switch
is used to reset all I/O devices, basic
timing controls, and registers (except index registers and
address registers). Digital input and digital-analog output
registers are not reset. RESET is effective only when the
processor-controller is not in a run state as indicated by
the run light being off.
The IMMED (Immediate) Stop Switch
stops the processor-
controller at the end of the main-storage cycle in progress
when the switch contacts close. All I/O devices, basic timing
controls, and registers (except index registers and address
registers) are reset. IMMED STOP also stops data channel
(cycle steal) operations which can cause loss of information
due to premature termination of a data transfer operation.
The Start Switch
initiates processor-controller operation as
specified by the mode switch. The processor-controller must
be ready as indicated by the ready light being on.
The Stop Switch
stops the processor-controller at the end
of the main-storage cycle in progress when the switch
contacts close. The processor-controller registers and 1/0
devices are not reset and data channel (cycle steal) operations
will continue until completed.
If an interrupt occurs on an interrupt level with higher
priority than any in progress at the same time STOP is
pressed, STOP must be pressed again to be effective. Once
the processor-controller has been stopped, pressing START
causes the program to resume operation.
CONSOLE
Dc:EJDGDI
IMMED
IDGB
INTR
STOP
Figure 3. Console Pushbutton Switches and Lights, Bottom Row
IBM 1801/1802 Processor-Controller
9
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