HP HP-67 - Page 263

Flags 259
o 1.111111111 All ones and all zeros
0.000000000 displayed alternately.
To stop the running program at any time, merely press (or any
key) from the keyboard.
How it works. After you have initialized the program by storing all
zeros in register R, and all ones in register R;, the program begins
running when you press [§. The 1and @ instructions
in steps 003 and 004 pause to display all ones from storage register
R;. The @ 0 instruction in step 005 clears flag FO. (Since the flag
is already clear when you begin the program, the status of the flag
simply remains the same.)
There is no after the routine begun by 3, so execution
continues through the 3 instruction in step 006 to the test,
@ ) 0, in step 007. The (3 0 instruction asks the question
“‘Is flag FO set (true)?”’ Since the flag has been cleared earlier, the
answer is NO, and execution skips one step of program memory and
continues with the 0 instruction in step 009. The 0 and
a instructions in steps 009 and 010 pause to display all zeros
from register R,. Flag FO is then set by the (J [SF) O instruction in
step 011, and execution is transferred to 3 by the G
instruction in step 012.
With flag FO now set, the answer to the test 0 (“‘Is flag FO
true?’’) is now YES, so the calculator executes the 3 instruction
in step 008, the next step after the test. After again pausing to display
all zeros, the flag is cleared, and the program continues in an endless
cycle, alternately displaying ones and zeros, until you stop execution
from the keyboard.
The above program utilized one of the two command-cleared flags,
so an ) [CF) instruction was required to clear it each time. However,
you should also be able to modify this program using one of the test-
cleared flags, F2 or F3, and shorten the program, saving one step
of memory.