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General Category => Discussion - EVE => Topic started by: lorcap on May 27, 2019, 12:53:35 PM

Title: BT815's PCLK stops clocking after 7340 periods
Post by: lorcap on May 27, 2019, 12:53:35 PM

Hi everyone,

I've been successfully using FT813 in my project for the past 3 years (custom SPI protocol implementation). We'd like to move to BT815. New PCB then, but same code base: BT815 doesn't show anything on the LCD (backlight is on, though). Can anyone help out?

Checking with a logic analyzer, SPI bus levels seem OK. Is there anything special to pay attention to when initializing the FT813 or BT815?

What I find strange is that signal PCLK stops clocking after exactly 7340 periods. Every time. It starts as soon as REG_PCLK is written.

To me, it looks like BT815 tries to talk to the LCD but gives up.

Pin DE is disconnected, DISP is driven high.

Thanks,
Lorenzo

Title: Re: BT815's PCLK stops clocking after 7340 periods
Post by: BRT Community on May 27, 2019, 02:04:03 PM

Hello,

The Initialization sequence for the BT81x series can be found in section 2.4 of the programmers guide:
https://brtchip.com/wp-content/uploads/Support/Documentation/Programming_Guides/ICs/EVE/BRT_AN_033_BT81X_Series_Programming_Guide.pdf (https://brtchip.com/wp-content/uploads/Support/Documentation/Programming_Guides/ICs/EVE/BRT_AN_033_BT81X_Series_Programming_Guide.pdf)

Please check you are following the recommended steps.
Would it be possible for you to provide a SPI capture of your initialization?



Best Regards,
FTDI Community

Title: Re: BT815's PCLK stops clocking after 7340 periods
Post by: lorcap on May 28, 2019, 11:51:39 AM

I tested more PCBs and I doubt the problem lays in the configuration because different PCBs have different behavior: some fails, other works perfectly.  When turning the same PCB on and off several times, it may fail or not at random. It really looks a hardware issue to me.

I also made the following test. If I stop any SPI activity after setting PCLK, the BT815 start clocking and then stop on a failing PCB.

Is there any pin I should check (apart from PD_N)?

Title: Re: BT815's PCLK stops clocking after 7340 periods
Post by: lorcap on May 28, 2019, 01:15:55 PM

I believe I found the culprit: myself. I didn't initialize the display list to any value before writing REG_PCLK. Now I send DISPLAY() and write REG_DLSWAP before REG_PCLK.

I think the behavior between FT813 and BT815 is different, though. I have never experienced any problem with my previous PCB.

Title: Re: BT815's PCLK stops clocking after 7340 periods
Post by: Rudolph on May 30, 2019, 08:25:06 AM

Quote from: lorcap on May 28, 2019, 01:15:55 PM

I didn't initialize the display list to any value before writing REG_PCLK. Now I send DISPLAY() and write REG_DLSWAP before REG_PCLK.

I think the behavior between FT813 and BT815 is different, though. I have never experienced any problem with my previous PCB.

Well I have a FT800 Programmers Guide.pdf from 2014 here and the given example for the initialization example is pretty much the same in the current BRT_AN_033_BT81X_Series_Programming_Guide.pdf.
And you are still not following it correctly.