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Simple Programming
127
zero for you to key in another burn. This sequence is repeated until
you successfully land (when the display will show you blinking
zeros), or you smash into the lunar surface (when the display shows
you the blinking crash velocity).
If you attemptto key in a fuel burn during any time other than the
one-second *'fire window,'' the rocket engine will shut off and you
will haveto restart it by pressing 5} . Restarting automatically uses up
five units of fuel and gives no thrust.
So press I3 now and try to land on the moon with your HP-67.
Stopping a Running Program
After you have successfully landed on the moon (or even if you have
crashed), you can stop the running program by pressing
or any
key on the keyboard. When you press any key on the keyboard while a
program is running, the program immediately stops and displays the
current contents of the X-register. The key function is not executed.
Looking at Program Memory
As you may remember from the program you created, loaded, exe-
cuted, and recorded onto a magnetic card in Meet the HP-67 at the
beginning of this handbook, a program is nothing more than a series of
keystrokes you would press to solve a problem manually. Whether
you load these keystrokes into the calculator from the keyboard, as
you did then, or from a magnetic card, as when you loaded the Moon
Rocket Lander program, the keystrokes are stored in a part of the
calculator known as program memory. When you slide the
W/PRGM-RUN switch to W/PRGM, you can examine the contents of
program memory, one step at a time.
First, press
(<) 000 to return the calculator to the beginning of
program memory. Then slide the W/PRGM-RUN switch
wrrGM [[HMruN
to W/PRGM.
The display should show
Program memory consists of 224 "'steps,"" which are numbered from
001 to 224, together with a top-of-memory marker, step 000. Program
memory is separate from the stack and storage registers.
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