Re: LZ: ZSHELL

To: list-zshell@lists.ticalc.org
Subject: Re: LZ: ZSHELL
From: Nathan Adams <nathana@goodnet.com>
Date: Mon, 09 Dec 1996 18:31:05 -0700
Reply-To: list-zshell@lists.ticalc.org

At 18:10 12/9/96, you wrote:
>On Mon, 09 Dec 1996 12:00:54 -0700,
>Nathan Adams wrote...
>>I learned Z80 assembly for zshell the way you have been trying to.  I
>>downloaded all the text files on zshell programming I could find.  The 
>best
>>way to learn, I think, is to read all that you can find and to practice by
>>writing simple programs.  Every time I start a new project I learn a lot 
>of
>>new things about assembly and zshell. A few things I still haven't figured
>>out are what or and xor do and what carry is.  So if anybody wants to
>>enlighten me as to their uses I'd be greatful.  I started assembly for
>>zshell only a few weeks ago and right now I'm writing simple text editor 
>as
>>practice.  Although it's turning out to be not so simple.  Anyway, a good
>>place to start is the TI-85 programming tutorial at
>>http://www.best.com/~jparker/ti-asm.html and the text files and links at
>>ticalc.org.
>
>About the or and xor command; if you or a number (the or command needs an 
>input in the acc), the value returned in the acc will have any bits set in 
>the same place as any bits in either the previous acc or the number you 
>or'ed it by.  Say the acc is %00001111 and you enter the command or 
>%11110000, the result will be %11111111 (because in the acc, bits 0-3 were 
>set, and in the number the acc is or'ed by, the bits 4-7 were set)
>
>xor'ing will do something similar, but not quite.  If any bits in both the 
>acc or the number you or'ed it by (From now on I'll just call it V!) are 
>the same (set or unset), then they won't be set in the final result (stored 
>in the acc).  Any bits where they are not the same, (i.e. one is set, the 
>other isn't) the result will have a bit set in that place.  So if the acc 
>holds the value %00001111, and you xor %11111111, the end result will be 
>%11110000.  This is good for encoding parts of programs (such as passwords 
>and stuff like that).
>
>The carry bit is pretty simple.  Any addition during which the result is 
>over 255, the carry bit is set to show that a number was carried over (to 
>the carry bit).  It is also used in some shifting and rotation stuff.
>
>I'd recommend the book "Programming the Z80," by Rodnay Zaks.  It's a great 
>book for learning the basics of assembly language, and it's specific to the 
>Z80.  It describes all of the commands that you may have questions about.
>
>Michael Wyman - SeaHorse Software
>wyma0012@gold.tc.umn.edu
>
>

Thank you very much, that explains a lot.
Nathan Adams
nathana@goodnet.com
"It is better to remain silent and be thought a fool,
than to speak out and remove all doubt."

Follow-Ups:

LZ: zshell string size prob.

From: Andrew Haninger <ahaning@freenet.columbus.oh.us>