Checksum: 60619
Path: utzoo!utgpu!mms
From: mms@gpu.utcs.toronto.edu (John J. Chew III)
Date: Mon, 8-Feb-88 01:16:21 EST
Message-ID: <1988Feb8.011621.1019@gpu.utcs.toronto.edu>
Organization: The Poslfit Committee
Newsgroups: comp.sys.handhelds
Subject: Re: Undocumented functions
References: <3255@super.upenn.edu> <3624@ihlpf.ATT.COM>
Reply-To: poslfit@gpu.utcs.UUCP (John J. Chew III)

In article <3624@ihlpf.ATT.COM> nevin1@ihlpf.UUCP (00704a-Liber,N.J.) writes:
> In article <3255@super.upenn.edu> mallow@linc.cis.upenn.edu.UUCP (Eric Mallow) writes:
> >  Does anyone know of any undocumented functions on either the HP-25,
> >TI-59, or HP-28c? Are there any undocumented features involving the
> >TI-59/PC-100C printer combination, or TI-59 card reader?
> 
> One of the undocumented opcodes on the TI-58/59 (I think it was 48) would
> allow you to modify the printer registers directly.  The way you enter this
> opcode is by going RCL 48 in program mode, then go back and delete the RCL.
> When this opcode is printed, it prints as "HIR", and the next line is the
> register number you want to modify (such as HIR 01).  These registers only had
> ten digits of precision (as best as I remember it), and would store non-negative
> integers only.  You could do some of the things you could do with normal
> registers, such as multiply into them, etc.

The HIR opcode allowed you access to the stack that was used to
hold values during HIeRarchical algebraic expression evaluation.
I vaguely recall finding them useful when memory was running low
and I wasn't doing anything with a complicated order of evaluation.

There was also something else I remember discovering about strange
things that happen if you step past the end of program memory
when the last instruction was a multi-step instruction.

If I could only find my notes or my 58C in my closet now... :-)

John Chew

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