Is it possible to have a GLCD without a chip select

[8bitman]

I purchased a JHD529 graphic lcd a few weeks ago, the part number is 12864F. On the face of it, it would appear to be pretty similar to most other glcd's based on the ST7920/1. I have it interfaced to a PIC 16F877A, with some additional circuitry to generate the required negative voltages. I can use the GLCD fine in character mode, but when I attempt to write to the screen in graphics mode I can seemingly only write to the first 19 lines (Y), but fully across the screen (X). Being fairly new to electronics and PIC/GLCD programming I went searching the internet. It would appear from all the documents that I read that most GLCD's are split into two individual chips which you have to select by setting chip select pins high. Thus in order to write to the lower half of the screen or the left / right side you set CS1 or CS2 high depending on the requirement.

This seems pretty straight forward until I realised that my GLCD doesn't appear to have any chip select pins. My question therefore is whether it is possible to have a GLCD without chip select pins, or if I have some really strange GLCD which should never have existed

Link to the short datasheet:
**broken link removed**

I also have the full datasheet but couldn't find it online to link to.

Thanks,
Paul.

 

[duffy]

I feel your pain. A couple of years ago I was writing code to drive an Optrex F-51405GNB-LW-ANN, and it had just such an arrangement with two completely separate driver subsystems, splitting the panel right down the middle, and I went through all kinds of contortions to get images to scroll smoothly across the boundary.

On that one, one CS line was high for the left, low for the right.

On yours, I don't see that there two controllers. There's two column drivers, yeah, but those don't cause problems, and anyway you know you can write all the way across - so THAT ain't it.

According to that diagram, you have just the one ST7920 doing all 64 rows high. Did you get the spec sheet for the ST7920? This will tell you a lot more than the crappy data from the LCD manufacturer.

 

[8bitman]

Thanks for the response Duffy, it is proving a difficult one to solve! - I have gone down the path you suggested and come across a post on another forum which demonstrated code to support the no chip select method. Basically you just have to write to 8 bit bytes consecutively one after the other instead of having to select which chip. This is pretty much the same as my understanding was already, however still doesn't explain why my code doesn't work

Still, thanks for the help, much appreciated. I am off for another session on the big 'G' to see if I can turn anything up.

Thanks,
Paul.