View Full Version : GDM12864 - Has anybody used this gLCD with the Prop yet? I'm having problems.

01-06-2009, 05:41 AM
I bought a few of these off ebay (yeah, I know, I went cheap) and have been having problems try to hook them up to a propeller. I'm using the KS0108 128x64 parallel lcd object from the parallax object exchange.

I can get display but it's a bunch of chinese letters and random text. I briefly saw a line get drawn for about 10 pixels then the screen refreshed and printed out more chinese characters. I'm fairly certain that I have everything hooked up correctly as I'm actually seeing output and it's changing (not the mention that I traced each connection about 100 times - but we've all had that excuse right?). I haven't verified that it works on other platforms so I'm not even sure if I have a valid device.

One thing that is worth mentioning is that a schematic I had incorrectly shows the backlight vco being connected to the +5vdc line. This is completely incorrect (and I've since sent the author a note regarding this) since it ends up dumping -9v onto the +5vdc line. After blowing off the wisps of smoke from my +5v regulator (and replacing it just in case) I started seeing output - only it's what I described above. I also noticed that one of the masked blobs on the board (U3) was very hot after shorting-9vdc to the +5vdc rail (gee, I wonder why). I hoping I didn't fry this guy - though a second device which was not hooked up wrong behaves similarly (with enough random differences to make me wonder if both were faulty). I'll try to post code and video later if that will help - but I was wondering if anyone has used these devices and/or had problems with them on the propeller. (Please see attachment for the datasheet I received with my purchase - and pretty much the only datasheet I can find on these animals)

Erik Friesen
01-06-2009, 06:12 AM
Are you absolutely positive that you are seeing chinese characters? The KS0108 chips do not have any characters built in.

soshimo said...
This is completely incorrect (and I've since sent the author a note regarding this)

I assume you are referring to the datasheet? I have received no email. The pinout diagram is for reference only per my display and I hope it didn't mislead you.

One thing to try is changing the tdelay within assembly. The code does not do a ready check. I suspect some cheap knockoffs of the ks0108 will require a longer delay.

01-06-2009, 08:00 AM
@Erik - I'm sorry Erik, I didn't mean to imply that your diagram was incorrect. I actually found a diagram for a different uprocessor (AVR) that I was using - don't ask me why I guess I was brain dead TBH I didn't look at your code http://forums.parallax.com/images/smilies/redface.gif, it just seem to work so well for others I assumed my problem wasn't software based, but hardware based. What you say about the timing make sense. The ebay listing does say that it's ks0108/0107 compatible so I'm assuming that it at least follows the same instruction set (again, didn't get that much into detail about it and didn't want to - that's why I ride on the shoulders of giants such as yourself :)).

I'll give the slow downs a try - from what I'm reading in other forums (AVR) that those cheap knocks offs actually have very bad refresh rates of almost as low as 200ms. That's crazy considering I was working on cell phones back in 2002 that had lcds with refresh rates of like 50ms and better (try porting a 20fps symbian game onto a brew handset - ha ha). Those were top of the line, of course, but I can only imagine that in the last 7 years there have been at least some improvements.

Again, sorry for the confusion, your documentation is sound and I was referring to another party not related to propeller development.