GLCD, how to choose.

[nuclear__]

Hi guys,
I'm designing a board based on 18f4550 to use it as development board for myself. I'm new to ccs. I'm tired of air wires etc so i want a board on my needs to add whatever i want and not a ready development board.

I want to place a glcd on board. It must be somehow big (at least 1.8") so ssd1306 is excluded and i want it for 3V3 operation. Resolution is not important. It would be nice if it is spi/i2c and not parallel but 4bit parallel is ok if there are no spi/i2c. And of course drivers should already exist since i can't create one yet.
I already bought one with ILI9341 which looks great and cheap but unfortunately i didn't find drivers for ccs. I found drivers for it in another C language and then tried to fix it, error by error but it is much above me.

Can anyone suggest me one? Will ks0108 work as is on 3V3? I read a datasheet saying 5V+-10%(bad) while high threshold was 2V(good) but it could be for the specific product. Even links would be appreciated.
Thanks

[Ttelmah]

Since the F4550, does not work at 3.3v, you have a problem....

4.2v minimum.
The LF can work at 3.3v, at 25MHz max


For 3.3v operation with USB, for full speed as an equivalent chip you want the 18LF25K50.

[nuclear__]

Yes I meant LF4550. I read somewhere that usb can work on 3v3 operation with external vusb and that max clock refers to core only.
Thanks for your tip, I will probably go to your safe advice (18lf45k50).

Any suggestion on i2c GLCD with library support?

[nuclear__]

Well I saw 18lf45k50 datasheet and find it somehow heavy. So I tried to work on breadboard with 18lf4550 (which I have already use) with 3V3 and confirmed that usb (full speed) works fine! Even at 2.6V !

[Ttelmah]

Yes, on the LF, USB will be fine down to 3v (2.6v, takes you below the legal voltage for USB transceiver drive - it'll work on some PC's not others).

However the point is that your clock rate will be limited to just 25Mhz at 3.3v.
It'll 'probably' work faster than this, but is not guaranteed, so trying is a recipe for disaster....
If your chip wants to run faster than this, you need a chip that is rated for faster operation at a lower voltage.

On the display, a huge amount depends on the temperature range that you want, and what power requirements you have. It's very common to find displays that work great at room temperature, but become unreadable as the temperature drops. Then the big problem - speed. If you want to draw a line across the diagonal of a display that is the size of your ILI unit, the line will 'touch' 400 pixels. The code then either has to have enough memory in the processor to hold a 'copy' of the display, change the bytes in this, and write these to the display, or has to read each byte in turn, change it, and write it back. For this single line, with display offering all these colours, 1200 reads and 1200 writes. Even if each can be done in a few uSec, just this one line is taking a significant part second. Start drawing text, or changing larger areas of the screen, and speed will plummet.

So, if you have to control it with a PIC, then the first thing to do, is decide on the _minimum_ resolution and number of colours you can use. Just reducing to 256 colours, cuts the amount of data involved to 1/3rd. Then also, with less data, you have the possibility of holding a copy of the data in the PIC, and speeding things by only writing - this is the FAST option in some of the existing glcd drivers. Otherwise you are going to find the speed of the display unacceptable for anything better than static displays. The alternative here is to look at a 'smart' LCD (more expensive, but then you only have to send commands to draw the object, and the display does the work - much easier and faster). Problem here is that few of these come in 3.3v versions. However it's worth realising that some actually have 3.3v regulators built in, and will talk to a 3.3v processor fine. So a unit like the 4D systems uOLED-128-G2, requires 4v minimum to run itself, but gives 3.3v at 50mA out which might be enough to run your other circuitry.

[nuclear__]

i hadnt realise that they need so much cpu power, i thought that they were all <<Smart>>. Thank you for your support .

[Ttelmah]

For text LCD's, probaby 80%+ are 'smart', using a clone of the standard Hitachi controller. For graphic LCD's, probably less than 1% are 'smart'. Most rely on the processor doing all the work, and if the display memory can be directly mapped into the memory map of the processor this is the cheapest way to work....

[temtronic]

Also when choosing a module, consider local availability ! Price is NOT the main reason to buy a module.
And, consider what others are using, say in your school, work group, peers, etc. Having someone else to talk to in person, looking at your project can help tremendously !


Jay

[nuclear__]