IBM Professional Series User Manual page 373

"RUNNING" indicates the processor is executing
instructions or could possibly be in the 370 wait state. The
storage and register locations can not be altered in this state.
The "ADDR-COMPARE" (Address Compare) state
indicates that an address compare match has occurred. This
will appear on the screen without user prompting. The
processor is stopped in this state. You would normally use
the Fl (Instruction Step) or F2 (Start) keys to exit this state.
When you press the F 1 key, the processor enters the
"INSTR-STEP" (Instruction Step) state. You would enter
this state to force the 370 processor to execute one 370
instruction with each press of the Fl key. The processor is
stopped in this state. You would normally use the F2 (Start)
key to exit this state.
When you press the F 1 key and the processor is in the wait
state, the processor enters the "ISTEP-WAIT" (Instruction
Step - Wait) state. The 370 instruction counter does not
advance in this state because the processor will not execute
instructions in the wait state. As in the "INSTR-STEP"
state, the processor is stopped. You would normally use the
F2 (Start) key to exit this state.
Fl Key - Instruction Step
You press the F 1 key if you want to have the processor
execute one instruction at a time.
If
the processor was in the
"RUNNING" state, pressing Fl has the same effect as
stopping the 370 processor, and the status area indicates the
"STOPPED" state. Each time you press the Fl key, the 370
processor will execute one 370 instruction. The status area
will indicate "INSTR-STEP." You would normally exit from
this state by pressing the F2 (Start) key.
Editing 370 Registers
The registers you would most commonly edit are the 370
General Purpose Registers (GPRs) and the 370 Program
Status Word Register (PSW). Both are displayed on the
screen.
B-4 VM/PC Users Guide