Data transfer through the LPT port...
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Author:  Syridian [ Tue Feb 15, 2005 0:15 ]
Post subject:  Data transfer through the LPT port...

Simple question really.

How fast do the current range of drivers write to the LCD's through the LPT Port?

Hmm maybe thats not so simple...

If data bandwidth were at a premium, how slowly could we write to the LCD without making it have too many problems?

OK.. I think I'm confusing the situation even more. I want to send serial data to an LCD at no greater than 3kbs, is this possible? I relise the screen updates would be really slow, I'm only looking to get get 1 frame a second on a 128x64 pixel screen, with minimal graphics. Or even just using a HD44780 compatible display. Oh, and yes, I realise there would need to be some serial/parrallel convertion electronics in place for this to work.

Author:  Henri [ Wed Feb 16, 2005 0:17 ]
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I don't know exact numbers but maybe something like 100-200 KBytes/s. Of course that's not sustained rate but only short bursts and depending of the screen to show.

It should be possible to write slowly too but some additional arrangements might be useful. Where do you have this slow transfer rates, some wireless stuff ?

Author:  Syridian [ Wed Feb 16, 2005 1:05 ]
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You can buy small serial data transmitters and recievers, and I'm looking at making a wireless LCD. However the data rate of these really cheap transmitters and recievers is only 3Kbs. I think it might be out of the realm of Graphical displays, however I'm suspecting that it wouldn't be a problem for a modified HD44780 driver to transmit a screen at those datarates.

Author:  Henri [ Sat Feb 19, 2005 18:08 ]
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Yes should be possible. Sounds like another interesting project to try...

Author:  Syridian [ Mon Feb 21, 2005 23:46 ]
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Is there currently any flow control on the LPT port? or is data just pushed to it, hoping that the display at the other end can read it correctly?

What I'm getting at is.... Would there need to be a special driver, or is there a way to make it work in hardware, using the LPT port flow control hardware? Maybe hold one of the input pins, until each byte is shifted through or something?

Author:  Henri [ Fri Feb 25, 2005 14:50 ]
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No flow control is used (in most current drivers). T6963C driver has support for reading back the busy flag before sending new data. This can be enabled in the driver configuration.

I suppose it should be possible to take advantage of the LPT port flow control but I haven't researched this more.

Problem with just polling some input pins is that if it's done in a blocking loop it can take too much cpu time. I know there is also interrupt pin in the LPT port but I don't know much of it and if it would be possible to use it.

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