Re: A89: faster LCD update on HW2 ?
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Re: A89: faster LCD update on HW2 ?
On Sat, Jul 15, 2000 at 23:06:33 +0200, Olle Hedman wrote:
>
> You probably already know this, but you can change how many scanlines the lcd
> has (will read), with port $600013. It containes ($100 - numberofscanlines).
> thats $80 for default.
This is what I know about $600013:
--snip---
$600013 ($80)
:7-0 LCD logical height =(256-n)
Tells the LCD hardware how often is should insert a '1' into
the screen row enable shift register and reset the DMA
pointer. The shift register is (or seems to be) cleared on
writes to this I/O-port. Each row takes, by default, 64 SLOW
cycles (about ~12.03kHz). (See $60001C.)
Note: The DMA reads ALL lines, whether they are visible or not!
--snip---
(The last line was added today... :) )
Also, does '89hw.txt' still claim that $600015:0 controls an oscillator and
$600015:1 is "LCD data enable"? According to my tests, it's vice-versa:
--snip--
:1 SLOW enable (used for LCD and timers above)
The ROM disables SLOW while enabling/disabling protection.
:0 Screen DMA enable, LCD blank ("white") if =0
HW1 calcs run ~10% faster when the DMA is disabled.
--snip--
/Johan
References: