Custom Characters on Parallax Serial LCD Displays

RobertW

Hello,
I see that the Parallax serial LCD displays can store 8 user-defined custom characters.· I was looking at the Jameco website for other LCD options and saw a few that were serial LCD's with a graphic image being shown next to some text on the screen.· If needed, is it possible to quickly·re-write the display's RAM to have more than 8 custom characters/ graphics?· I imagine that the re-write speed depends on the communication speed but any ideas how fast this could be done?· Anything similar to the re-fresh rate on a TV or computer monitor, etc?· I am thinking that 'images' could be stored in a Propeller's data table·and called as needed.· Has anyone done this?

Thanks,
Rob W.

P.S. Still kicking myself for not picking up 1 or 2 of the 4 x 20 displays on sale for $22 a few weeks ago. Ahhh!

Peter Jakacki

The limitation is due to the LCD driver chip itself in that it has only 8 programmable characters, the rest are in ROM. Yes, you can rewrite them but the speed would be limited by the baud-rate and also that would change how the character for that "code" looks globally. This is not a computer monitor where you may have control or time to manipulate programmable characters or bit-mapped graphics during refresh.

Maybe you just saw some predefined ROM characters like this one below.

*Peter*

photomankc

I'm glad I grabbed the 4x20 on sale. That's going to be handy to have on hand for a simple display and debug output. I will say I hate the way 'scrolling' is done on it. The simple return to the top and plow over existing text method makes scrolling through data a pain and you operate blind so there is no way to ask where the cursor is. Also the automatic line wrap at the end of each line can make it a little tricky. It's better for fixed field displays where you are always writing to the same location with updated data.

I doubt you would get very far trying to make it into a graphics display.

Peter Jakacki

The controller on my 4x20 LCDs that I design has a lot more in the way of user control. Not only does it emulate the Seetron and the Parallax displays but it also has quite a lot of other features such as the scrolling option and selectable line wrap, variable backlight, bargraph mode and buzzer drive. There are no jumpers or pots to set (hate em), the whole thing is auto-polarity (RS-232 or logic) and auto-bauding or I2C while the contrast is set by a tiny push-button or user commands. Pretty much does everything and holds user defaults in EEPROM and is smaller. Trouble is I don't sell one offs as all the other ones have retail distribution channels whereas I normally sell in batches directly to OEMs.

*Peter*

photomankc

So you just want to tease us then? [noparse];)[/noparse]

RobertW

@photomankc
You wrote that it is difficult to know where the cursor is. Is it possible to keep track of the number of characters in a string by using a variable, or keep track of the cursor location in a variable / memory location?

What started this, as I originally wrote, is that I saw a display with a spedometer type graphic and a speed printed in text on the right side of the graphic. There was an arrow in the graphic.

Here is the link:
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=693812&

I was thinking that if the user-defined characters could be updated fairly quickly then the arrow in the graphic could 'move' relative to the speed being show in text. I understand that this would require many pre-defined characters in a data table that might be called up and sent to the LCD as required. This is just what I had in mind when I posted may original message. Just wondering if it was possible or pointless. I know that the graphics/image would be nothing to compare to a TV or VGA output but was just curious.

Thanks.

photomankc

Certainly you could, in your own driver, track the cursor position by watching every call and what it does but that's a big pain in the butt. You could also maintain your own memory image of what should be on the display at that moment and put it on the screen. I would say there are better displays to use if you really want to get graphics out of them.