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Section 14: Flags217
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When flag 21 is clear, it is assumed that you do not have a printer in your HP-41C
system. Programs that contain specific printing functions (refer to the printer
owner’s handbook) will run properly but will not print. With the printer plugged
in and flag 21 clear, execution (in a program) of one of the print functions results in
the PRINTER OFF display. But if the
printer is not present—the display will show
NONEXISTENT. In both cases, execution
halts.
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On the other hand, if flag 21 is set, the calculator assumes that a printer is present
in the system and the HP-41C attempts to print. If a printer is still not present,
execution of specific print functions result in the
NONEXISTENT display. In addition, the
standard HP-41C functions VIEW , AVIEW
and PROMPT (which normally cause printing when flag 21 is set
and the printer is present) will perform their normal functions and will also halt execution.
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The status of this flag is set to match the status of flag 55 (the printer existence flag)
each time the HP-41C is turned on. (Flag 21 and 55 are both set if the printer is present
and clear if not.)
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Data Entry Flags
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There are two flags in the HP-41C that are used to detect keyboard data input: the
numeric input flag (22) and the ALPHA input flag (23).
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Flag 22 is used to detect numeric data input. The HP-41C automatically sets flag 22 when
numeric data is entered from the keyboard.
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Flag 23 is similar to flag 22 except that it is used to detect ALPHA data input. The
calculator sets flag 23 when ALPHA data is entered from the keyboard.
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Both flags 22 and 23 are cleared each time you turn the calculator on.
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Example: Computer programming student Jill Bitter is a little
confused about how to use hexadecimal numbers (base 16). Her teacher suggests
that she write a program on her HP-41C to convert hexadecimal numbers to
decimal numbers. Jill’s first program is below. It converts a single-digit
hexadecimal number to decimal.
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