[A83] Re: LCDBusy

To: assembly-83@lists.ticalc.org
Subject: [A83] Re: LCDBusy
From: "D Weiss" <dwedit@hotmail.com>
Date: Mon, 19 Mar 2001 10:01:39 -0600
Reply-To: assembly-83@lists.ticalc.org


>From: "Robert Maresh" <gardenerbm@netzero.net>
>Reply-To: assembly-83@lists.ticalc.org
>To: <assembly-83@lists.ticalc.org>
>Subject: [A83] LCDBusy
>Date: Mon, 19 Mar 2001 09:14:07 -0600
>
>Why do we use this routine:  (33 clocks)
>
>                  LCD_BUSY::
>                      PUSH    AF
>                      inc     hl
>
>                      dec     hl
>                      POP     AF
>                      RET
>
>
>
>When we could use this one: (32, could change it to be 33?)
>
>LCD_BUSY:
>
>   halt
>   halt
>   halt
>   halt
>   halt
>   halt
>   halt
>   halt
>   ret
>
>Sure, it's four bytes larger, but I thought halt saves on battery life.  Is 
>this one of TI's oversights, or am I completely wrong???
>

Halt waits 1/200th of a second, as someone mentioned already.  If you add 2 
halts to a main loop of a game, you will notice a major speed difference. 
And if you HALT when interrupts are disabled, it just crashes.

That and it takes more bytes, and there is a really good reason to wait 
LONGER rather than shorter.

If you don't wait long enough for the LCD to catch up, you get an ugly 
staircase effect of horizontal bars not updating randomly.  Even ION itself 
doesn't wait long enough on TI83 ROM 1.10 (the new style TI83).
>Bob Maresh
>
>

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