Re: [hatari-devel] TT hardware memory information

[David Savinkoff <dsavnkff@xxxxxxxxx>]

----- Thomas Huth wrote:
> Am Wed, 16 Mar 2016 17:25:16 -0600 (MDT)
> schrieb David Savinkoff:
> 
> > ----- Thomas Huth wrote:
> > > On 16.03.2016 02:10, Roger Burrows wrote:  
> > > > The TT has a sync mode register at the same address as the ST
> > > > (0xff820a). However, it's not set up the same way.  TOS3
> > > > initialises it to 0x01 very early in initialisation, and it is
> > > > not updated elsewhere.  While getting EmuTOS working on my TT, I
> > > > discovered that, if this is set to 0x00 or 0x02 (like it would be
> > > > on an ST), there is NO output to the screen: my LCD monitor
> > > > remains blank, although it does detect the correct screen size
> > > > and refresh rate.  
> > 
> > I think the TT is doing exactly what you said:
> > The TT puts out a black picture (blanked) with hsync an vsync running
> > as usual. Thus, if you want a black screen you zero the bit.
> 
> What should be the purpose of that? To get a black screen, you could
> also simply set the palette to zero.
> 
> > This should be tested because I'm sure a demo will be made, if it
> > isn't already.
> 
> Who's going to do that? And why?

After reading the extra info you said here about the mono detect,
I can assume to add to what I said (as a reasonable possibility).

When the mono detect is used for sync and 0xff820a bit 0 is
in sync-mode, the STE uses an external signal for synchronization;
however, when there is no external sync-signal the STE
provides its own with a black screen. This makes sense as
phase locked loops can be lightly pulled by an internal oscillator
that may be over-ridden by a forceful external signal.

I propose that someone with an STE discover some new stuff here.

I'll now read the info in the link you provided below.

> > > > In the "Atari TT030 Hardware Reference Manual", June 1990, there
> > > > is a note that bit 0 of this register is 'set to 1'.  There is no
> > > > further explanation.  
> > > 
> > > IIRC, I once read somewhere that bit 0 of this register has been
> > > inverted on the TT, i.e. when it is set to 0, that means the sync
> > > signals are taken from external source, and 1 means that they are
> > > generated from the shifter.  
> > 
> > I looked at the schematics and could find no means to accept hsync or
> > vsync or any video signal from an external source. Can it be done?
> 
> I never looked into that external synchronization stuff before, but at
> least on the STE, it seems like it was possible, according to:
> ftp://untergrund.net/users/ggn/Atari%20HQ/Documents/Atari/TECHDOCS/STE/FSG/STE_CH2.TXT
> 
> "2.11  GENLOCK AND THE STE
> 
>  The ST (and STE) chip set have the ability to accept external sync. This is controlled by bit
>  0  at FF820A, as documented in the ST Hardware Specification. This is provided to allow the
>  synchronization of the ST video. In order to do this reliably the system clock must also be
>  phase-locked (or synchronized in some other way) to the input sync signals. No way to achieve
>  this was provided in the ST. As a result, the only GENLOCKs available were internal
>  modifications (usually for the MEGA).
>  The STE, on the other hand, allows this to be done without opening the case. To inject a system
>  clock ground pin three (GPO) on the monitor connector and then inject the clock into pin 4
>  (mono detect)."
> 
> So I assume it was either similar on the TT like on the STE, or you
> needed a further hardware modification like on the ST.
> 
>  Thomas
> 
>