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FEZ-Disp vs Large Graphical Display


#1

I have two displays I purchased from GHI, and I can only get one of them to work:

B&W 128x64-Pixel Display http://www.ghielectronics.com/catalog/product/208
Graphical 3.6" Display (no longer for sale)

The 3.6" display works great (beautiful display, BTW), but the smaller FEZ-Disp I cannot get to work. I’m wondering if they use the same controller, meaning I can use the same driver for both?


#2

The code for the two displays is NEARLY the same… NEARLY.


#3

I just got one of the 128/64 BW displays on sale, and the provided driver works just fine. I have not tried the simple graphics driver yet.


#4

I got the display working. The important differences are the ChipSelect_ActiveState (which must be true on this display, versus false on the larger display) and the COM OUTPUT DIRECTION initialization which must be 0xC0 on the larger display, and 0xC8 on the smaller display.

The response time on the smaller display seems to be slower, but I haven’t played with it a ton yet. I do wish there was a way to turn on/off the LED backlight.


#5

Further, the SPI configuration in the GHI driver seems to have EXTREMELY conservative values for the SPI configuration. I changed the CS setup time to 1ms, the CS hold time to 1ms, and the clock rate to 3mHz and the display works without issues.

Just how far can the SPI clock be pushed on these displays, Gus? I’ve gone all the way to 30mHz, but it doesn’t seem to change anything. It seems unlikely that it could really be working at that frequency…?


#6

There is a limit on FEZ max clock and the divider, so if you set it to 30Mhz then you will not necessary get 30Mhz out


#7

Right, I believe I read somewhere that the limit for the SPI clock is 1/8 the input clock for the MCU. Would this make the SPI max 1.5 MHz?

Also, is there a datasheet somewhere for the controller used in this display?


#8

I think it is 1/2 72Mhz.

So when you set it to 30Mhz … from 72Mhz, 72/3 = 24Mhz
Make sense?


#9

All I know is I’ve got it set to 10000 Hz right now, and it’s working great :slight_smile: