Re: Weird issue with the Pet 2001-N

From: Rhialto <rhialto_at_falu.nl>
Date: Sat, 6 Apr 2019 12:38:01 +0200
Message-ID: <20190406103801.GC7533_at_falu.nl>
On Fri 05 Apr 2019 at 07:28:24 +0100, David Roberts wrote:
> It could also be the octal read buffer from the screen RAM dropping a bit
> rather than the main RAM itself. The 'Y' gets entered onto the screen
> correctly. I can't just remember off hand whether the command line is
> constructed in main RAM or read from the screen RAM when RETURN is entered.

Yes, the normal procedure is that whatever you type is collected in
screen memory. Once you hit RETURN, the text is read from the screen
memory and put into the INPUT buffer. (At least that is what the Basic
editor and the INPUT statement do). There is a location which remembers
the initial cursor position (so that if there is a prompt with INPUT
"prompt", A$, you get only what you typed into A$). But that location is
reset once you use the cursor up or down keys. That explains what
happens when you move the cursor wrong and then back, upon answering an
INPUT.

Once upon a time I looked deeply into this. Did you know that you can
also open a file on the keyboard (OPEN 1,0) and INPUT#1 from it? That
works out slightly differently than a normal INPUT statement.

Similarly you can OPEN the screen (OPEN 1,3) and PRINT# to it, but also
GET# from it, and I think also INPUT# from it.

-Olaf.
-- 
___ Olaf 'Rhialto' Seibert  -- "What good is a Ring of Power
\X/ rhialto/at/falu.nl      -- if you're unable...to Speak." - Agent Elrond


Received on 2020-05-29 21:12:39

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