Section 9: Program Interruptions147
Keystrokes Display    
  The program stops so you can key in the radius of the sphere.
  21.22 _    
  The radius of the spherical balloon.
  The answer in cubic feet.
  Display remains form previous execution.
  1.905 _    
  The radius of the ping pong ball in centimeters.
  The volume of the ping pong ball in cubic centimeters.
In the next section (section 10), you will see how ALPHA strings can be used to make prompting for data simple—your programs can actually ask you for data.
Using PSE (Pause)
The PSE (pause) instruction executed in a program momentarily interrupts program execution and displays the contents of the X-register. The length of the pause is slightly less than one second, although more PSE instructions in subsequent lines of a program can be used to lengthen viewing time, if desired.
Each time a pause is executed, the PRGM annunciator blinks one time. This lets you know that the program is running—even during a pause.
During program execution, the only keys that are active are R/S and ON . However, during the execution of a pause, of a string of pauses, the entire keyboard becomes active. You can actually input data to your program during a pause.
Pressing data entry keys during the execution of a pause causes the pause instruction to be executed again (or until you have completed the data entry). Data entry keys are: ALPHA , USER , g , 0 through 9, CHS , EEX , and all ALPHA characters.
Pressing any other keys during a pause, that is, any keys not associated with data entry, causes the pause to terminate and program execution continuous. The pressed function is executed.
Keyboard Stops
As you know, pressing R/S form the keyboard during a running program halts that program. The program may halt after any line—if you set the calculator to PRGM mode after a program is halted, you will see the line number and the instruction of the next line to be executed.