Re: Mix LGR and Text?

[bieling@terra.es (Jorge Chamorro Bieling)]

Linards Ticmanis <ticmanis@gmx.de> wrote:

> AFAIK, you store certain values in the last few bytes of the visible 
> screen and make sure those values are nowhere else in your screen. Then
> you keep reading some unconnected I/O location. Since nothing is driving
> the data bus when you read those, the data that the video display 
> circuitry put on the bus will still be there for the CPU to see. As soon
> as you see your data, you're locked in and then you only have to keep
> your cycle counts.

I thought the ram's output would be tri-stated on the data bus if the
cpu's read was not addressing it... so this must have to do with the
capacitance of a data bus that has just been released (tri-stated) and
is being driven by nobody, you mean ? Though the data must remain there
for 500 nSec more for this to work...

What a wonderful trick !!!. Who managed to discover this ?

> Given that for example on the Atari 2600, all programs have to do stuff
> like this to get anything to display at all, and given that people 
> nevertheless managed to cook up about a thousand games for the thing,
> I'd say there is quite a lot you can do -- if you're masochistic enough
> for this kind of coding, that is.

Can you tell me more? what's the deal with the atari 2600 ?

Jorge.