Default baud rate incorrect?

[zeroping]

https://github.com/adafruit/Adafruit_CircuitPython_SharpMemoryDisplay/blob/3860f11bebcf4df94e2c180a26a809adaa4ccac6/adafruit_sharpmemorydisplay.py#L77

It looks like the default 'baudrate' (which is also used in the examples) is set to 8 MHz. When this is passed into busio.SPI.configure(), it's stated that it's the desired clock rate in Hertz.

The displays seem to be spec'ed for 1 MHz or 1.1 MHz though: 144x168 96x96

Should this default be 1MHz? Or am I missing something?

[ladyada]

looks like 2 MHz should be the max, did you try it at 8?

[zeroping]

I did, or at least, I've asked my hardware to do so, although I have not yet confirmed the output clock frequency with a scope or logic analyzer. It does appear to work just fine.

I'm more worried about running it outside of the spec, which I'm still reading as 1.1 MHZ (page 12 of the LS013B7DH05 datasheet, fSCLK) or 1 MHz (page 12 of the LS013B4DN04 datasheet, fSCLK). I'm curious where you're seeing 2 MHz - maybe an updated version of the datasheet, since the displays appear to handle running faster?

I'm just initializing adafruit_sharpmemorydisplay.SharpMemoryDisplay with a baudrate argument in my code for now, but I figured I'd mention that the default is technically too fast.

[ThomasBurgess2000]

I'm just initializing adafruit_sharpmemorydisplay.SharpMemoryDisplay with a baudrate argument in my code for now, but I figured I'd mention that the default is technically too fast.

What is the exact argument you used?

[zeroping]

adafruit_sharpmemorydisplay.SharpMemoryDisplay(spi, scs, WIDTH, HEIGHT, baudrate=1000000)

I have it working quite nicely in my project. Cute little display. I love that it can hold state with almost no power consumption.

[ladyada]

tweaked to 2mhz :)

[caolan]

This change makes a huge difference to the screen update speed. It seems very sensible to set the default value to match the maximum in the datasheet - but now I'd like to draw on your experience to see how far I can push my luck.

@ladyada, @zeroping have you had any reports of hardware problems using the higher clock frequency over the last 11 months?

@makermelissa I notice you decreased the speed to 8MHz at one point. Was that in response to any hardware problems that you can recall? Did you make any measurements to arrive at the 8Hz number?

I'm asking because I have some applications that really benefit from higher clock speed, but I don't want to damage people's other peoples displays if they try to run them!

[ladyada]

it seems to vary by screen. 2mhz is always recommended!

[makermelissa]

I think I was having problems with speeds over 8MHz. Like @ladyada said, it can vary by screen.

[caolan]

Thank you for your responses.

I also contacted someone at Sharp. They obviously cannot warrant anything outside the specified limits, but said it may be ok if the operating temperature can be controlled. The standard mean time between failures is 50KHrs at 25C, but increasing the clock speed will increase the internal temperatures and ultimately lower the functional life of the display.

I completely agree this library should follow the spec (at least by default). But I might suggest Adafruit update the video demo of this display on their website to use the lower clock speed from the datasheet. Otherwise, people will buy this screen with an unrealistic expectation of it's performance.