Rotary Switches - IBM 1800 Operating Procedures Manual

ROTARY SWITCHES (Figure 4)
The Display Address Register Switch is used to select a
channel address register or storage address register for
display in the address register lights.
DISPLAY
ADDRESS REGISTER
CAR 0
SAR
CAR 1
CAR 2
CAR 14 CAR 3
CAR 13
CAR 4
CAR 12 CAR 5
CAR 11 CAR 6
CAR 10
CAR 7
CAR 9
CAR 8
DISPLAY
XR2
DATA REGISTER
XR3
XR1
SC
Q
1
RUN
MODE SW
S I W/CS
TRACE
SI
LOAD
SSC
I
DISPLAY
SS
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Figure 4. Console Rotary Switches
10
IBM 1800 Operating Procedures
The Display Data Register Switch is used to select the
Q-register (which is the A-register exteIlsiun), and index
register, or the shift counter for display in the data register
lights.
The fir/ode SU' (Switch) is used in conjunction with START
I
to extend operator control of the processor-controller. The
function of each position of the mode switch is described
in the following paragraphs.
DISPLAY is used to display the contents of main storage.
Pressing START with the mode switch on DISPLAY
causes the data at the address specified by the
I-register to be displayed in the B-register lights.
The I-register is incremented after each display.
Pressing START successively displays the data in
ascending main storage locations.
LOAD is used to load main storage locations or the
I-register. Pressing START with the mode switch
on LOAD causes the contents of the data entry
switches to be stored at the address specified by the
I-register. (The processor-controller must be in a
stopped condition.) The I-register is incremented
following each load operation. Pressing START
successively loads the contents of the data entry
switches into ascending main storage locations.
Pressing LOAD I with the mode switch on LOAD
causes the contents of the data entry switches to be
stored in the I -register.
TRACE is used to initiate an interrupt on the lowest priority
level after the execution of each instruction (except
execute I/O instructions). This position of the mode
switch is usually used for program debugging.
RUN is used for normal program operation. Pressing START
with the mode switch on RUN initiates program
operation of the processor-controller.
SI W /CS (Single Instruction With Cycle Steal) allows
execution of one instruction each time START is
pressed. Data channel (cycle steal) operations can
occur during execution of the instruction.
SI (Single Instruction) allows execution of one instruction
each time START is pressed. Data channel (cycle
steal) operations are
preventede
SSC (Single Storage Cycle) allows one main storage cycle
each time START is pressed. Single storage cycle
operations (usually called single cycle operations)
can be used in conjunction with the cycle lights
to step through instructions and anaiyze processor-
controller operation.
SS (Single Step) allows one basic processor-controller clock
cycle each time START is pressed.