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HP -28S Manual Page 300

Advanced scientific calculator.
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On the HP-28S each of these dual roles is separated-there is no
stack lift disable. A command line completely distinct from level 1
(the UX-register U ) is used for command entry. ENTER is used
only to
process the contents of the command line-it does not duplicate the
contents of level
1.
Note, however, that the
I
ENTER
I
key will execute
DUP (which copies level 1 into level 2) if no command line is present.
This feature of
I
ENTER
I
is provided partly for the sake of similarity to
previous calculators.
Prefix Versus Postfix
HP-28S commands use a strict postfix syntax. That is, all commands
using arguments require that those arguments be present on the stack
before the command is executed. This departs from the convention
used by previous RPN calculators, in which arguments specifying a
register number, a flag number, and so on, are not entered on the
stack but are entered
after
the command itself-for example, STO 25,
TONE 1, CF 03, and so on. This latter method has the advantage of
saving a stack level, but the disadvantage of requiring an inflexible
format-STO on the HP-41, for example, must always be followed by
a two-digit register number.
Similar operations of the HP-28S are closer in style to
indirect
opera-
tions on the fixed-stack calculators, where you can use an
i-register
(or
any register, in the case of the HP-41) to specify the register, flag
number, and so on, addressed by a command. You can view STO,
RCL, and so on, on the HP-28S as using level 1 as an
i-register.
RCL,
for example, means urecall the contents of the variable (,register')
named in level
r -
equivalent to RCL IND X on the HP -41.
You should be aware also that most HP-28S commands remove their
arguments from the stack. If you execute, for example, 123
'X'
STO,
the 123 and the 'X' disappear from the stack. Without this behavior,
the stack would be overloaded with uold u arguments. If you want to
keep the 123 on the stack, you should execute 123 DUP
'X'
STO.
B: Notes for HP RPN Calculator Users
299

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