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LCD with 640x480... Possible?
http://forum.lcdinfo.com/viewtopic.php?f=6&t=1096		 Page 1 of 1
Author:  Myscha [ Wed Mar 09, 2005 19:01 ]
Post subject:  LCD with 640x480... Possible?
Hi everybody!

Could it be possible to connect the following display via a S1D13501 to the parallel port? Theoretically it is possible, but what about the cpu-usage? Will it increase very much or will it still be possible to work and play with the pc?
A driver for LCDInfo will be needed, but that shouldn't be the problem, i think... Or am i wrong?

Datasheets can be found here:
http://www.infinetivity.com/~jsampson/l ... 4148P1.GIF
http://www.infinetivity.com/~jsampson/l ... 4148P2.GIF
http://lcdhype.mod-extreme.info/lcdhype ... 33&index=0

Myscha
Author:  coorz [ Thu Mar 10, 2005 0:07 ]
Post subject: 
Sure looks that SED1351 could drive that display however i don't think LPT would be fast enough to supply that much data to a display that size.
USB might be a good alternative....
Author:  Myscha [ Thu Mar 10, 2005 0:16 ]
Post subject: 
One of the problems is, that i'm not really good in programming. I don't know whether i am able to write a working driver for usb or parallel...

Would anyone of you help me, if i'll get problems with programming?
Author:  Myscha [ Thu Mar 10, 2005 20:25 ]
Post subject: 
I have now read some articles and think it doesn't really matter whether the display is connected to lpt or usb. lpt has a datarate up to 2mbyte/sec. and the FTDI FT245BM has only 1mbyte/sec....
Author:  Henri [ Sat Mar 12, 2005 1:00 ]
Post subject: 
So to connect SED1351 to outside world you would need a 16 bit address bus, 8 bit databus and some control lines. This can be done with parallel port by using some latches to store the address. Of course this might not be that fast and with big display like 640x480 it might be a problem. But I suppose it would have to be tested to find out. Anyway using this kind method it's not possible to reach near the theoretical data transfer speeds.
And high cpu consumption becomes a problem with large lcd's in parallel port.

But if you have a SED1531 controller it's not expensive to build the interface to LPT port to try. Of course some programming is required like the LCDInfo driver but LCDInfo should have no problem supporting this.

USB might work better but currently I don't have a usb controller solution to suggest.
Author:  Myscha [ Mon Mar 14, 2005 13:26 ]
Post subject: 
I didnt' see before that there is a adressbus needed to communicate with the µ-controller...

Another idea: what about the HD61830? What is the maximum resolution of it? In the datasheet "512k dots" is written. That would be enough, i think (640x480=307200). Perhaps it is possible to drive the 640x480 lcd with that controller!? What do you think about that idea?
Author:  Syridian [ Tue Mar 15, 2005 0:23 ]
Post subject: 
I guess the question is how quickly do you wish to update the display. The method Henri described would be quite slow. concidering that you have 3 bytes of data to write to just to address one memory location. As normal with me, I haven't read the data sheet, so what follows is verbal garbage, and theortical stuff....

If each memory location stores a fully byte, 8 pixels either horizonal or vertical, then 640x480=307200, Divide that by 8 for the 8 bits of pixels per write, =38400 and then multiply that by 3 to get the data writes to achieve the full screen write, =115200. Ok.. So thats that data bytes needed to be written out of the LPT port per screen. Someone said eariler that the LPT port is capable of 2Mbytes/s transfers? Cool. So, 2097152/115200= just over 18 frames per second.

Seems acceptable to me, for a data display anyway. Although I would hate to see the CPU usage for it Concidering that doubling the size of an LCD Quadruples the amount that needs to be processed. Sure, if the Computers main task is to display that data, then CPU usage isn't a problem. But if displaying that data isn't a priority, then you really have to ask yourself if it's necessary to have such a large display. :)

However... standard disclaimer... Everything above was thoeretical crap, done without even reading the datasheet...
Author:  Myscha [ Wed Mar 16, 2005 0:23 ]
Post subject: 
And could it be easier and better with the HD61830 controller? What do you think?
Author:  Henri [ Wed Mar 16, 2005 18:37 ]
Post subject: 
I don't think one HD61830 could drive this large (in vertical direction) display. I remember there was some way to cascade HD61830 but still this doesn't sound that good solution here.
Author:  Myscha [ Wed Mar 16, 2005 20:36 ]
Post subject: 
In the datasheet is written that the HD61830 can drive displays with up to "512k dots". And mine has 307200 dots. If i knew where to get one of the HD61830 i would try, but they are no more produced and hard to get.
Author:  Henri [ Fri Mar 18, 2005 1:10 ]
Post subject: 
Yes I can also see the mention of 512k dots. But I also now checked the datasheet and it says 1/128 dutycycle maximum. So I think the panel can only be 128 pixels high with one HD61830.
Author:  Myscha [ Fri Mar 18, 2005 11:02 ]
Post subject: 
That's right, yes. But what does that mean: dutycycle? I read that, too. But i don't know what exactly that means.

I think it can be 2 times 128 lines, because of the 2 serial outputs, one for the upper and one for the lower half of the display.
Author:  Henri [ Wed Mar 23, 2005 21:36 ]
Post subject: 
When driving a lcd display it is driven one row at a time. So when there are 128 rows you drive one row 1/128 of the time -> 1/128 dutycycle.

Myscha wrote:
I think it can be 2 times 128 lines, because of the 2 serial outputs, one for the upper and one for the lower half of the display.

You could be correct.
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