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Forum Index : Microcontroller and PC projects : E-64 Random white screen phenomenon
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| LouisG Senior Member  Joined: 19/03/2016 Location: AustraliaPosts: 129 |
Hi all! Haven't posted for a while. I am using three 64-pin Micromites on a pilot process plant. 1. CGMicroboard2 + ILI9341 + 14xDO + 2xFI + 2xDS18B20 2. E-64 + ILI9341 + 14xDO + 2xFI + 2xDS18B20 3. E-64 + ILI9341 + 16xAI + 17xDO Each is supplied with 5V from it's own plugpack. The software in each works exactly as designed. None of the three use the touch facility. Occasionally, without warning, the screen of an E-64 shows a permanent white screen. Normal operation can be resumed only by momentarily interrupting the 5V supply to the E-64. Once when a white screen showed I carefully unplugged the screen and plugged in a spare one. It showed white too. Swapping CGM2's plug pack with an E-64's made no difference. I haven't yet seen a white screen on the CGMicroboard2. The one difference between the CGM2 and the E-64s is that the screen of the CGM2 is directly plugged in at the circuit board, whereas the screens of the two E-64s are each on an umbilical of wires about 30cm long from their circuit boards. I suspect that serious RFI from power contactors quite nearby is being picked up by the umbilicals. While building and testing No. 3 above, I unintentionally touched one of the screen pins. Suddenly the screen went permanently white, as described. Restoring it was by momentarily removing power. I repeated bringing up the white screen while MMEdit was connected and tried Geoff's famous Print 1/7. Lo and behold the proper result appeared, meaning that the Mite's processor was still running normally. So what was locking up? It appears that interference is entering via one of the display screen's wires. The screen is display-only (no touch connected or configured) and is essentially an output device. It is not the screen that is locking up nor is it the microprocessor. It's not the firmware either (it restarts and runs normally). Is RAM being affected? Is it some peripheral circuit on the chip? Ideally, if the effect of such interference were only fleeting instead of permanent the Micromite would be that much closer to being bulletproof. I can't obtain more info at present as the pilot plant is overseas (I am in Brisbane). Have to wait till planes are flying again. Keep well everybody! Louis PS. This is not a request for help in tracking down sources of RFI. - |
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CaptainBoing Guru  Joined: 07/09/2016 Location: United KingdomPosts: 2171 |
Sounds like it might be a termination issue - have you missed out any pullups? try a 10K pullup on each wire anyway at the display end of the umbilical. If you can't get to the unit, could you make up a board (with the pullups) to go in-between the display and the cable and send it to them? Also, simple and cheap "suck it an see" for RFI - can you loop the umbilical through a ferrite ring or get one of the clamp style ones around it? Send one of those too. Edited 2020-04-11 19:10 by CaptainBoing |
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| LouisG Senior Member Joined: 19/03/2016 Location: AustraliaPosts: 129 |
Thanks Captain. I can try both. ... L. |
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Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3308 |
Care must be taken with display panels that do not use touch. In this case the touch Chip Select signal must be configured in MMBasic or disabled by a permanent connection to 3.3V. If this is not done the unconnected Chip Select pin will float causing the wrong controller to respond to commands on the SPI bus. Could this be the issue? Geoff Geoff Graham - http://geoffg.net |
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| LouisG Senior Member Joined: 19/03/2016 Location: AustraliaPosts: 129 |
@ Geoffg I just checked my wiring diagrams. The T_CS (Touch Chip Select) pins of the E-64s are indeed floating! Thank you very much, Geoff! CaptainBoing's idea was on the right track with pullup resistors but I doubt if I would have thought of including the touch pins. Definitely worth including in a Tips 'n Tricks page if ever one is started. ... Louis - |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9755 |
Sounds like the T_CS pin floating is your issue. Please let us know if that has indeed fixed it. There were some issues with voltage-drop on the big LCD's a while back, but the wee SPI ones draw very little current and they normally just work every time, right out of the box.  I would encourage you to NOT hot-swap LCD's to test if the LCD is working in future. That procedure could potentially damage your LCD and perhaps the MM too. It ultimately won't work anyway, as part of the start-up sequence is the MM pulsing the reset line to reset the LCD controller chip, and then sending initialisation commands to the controller. Neither of those will happen if you hot-swap the LCD module. It is. Page 18 of the standard manual, under "LCD Displays" chapter: This means you with your LCD where you are not using the touch part. Edited 2020-04-12 12:42 by Grogster Smoke makes things work. When the smoke gets out, it stops! |
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| LouisG Senior Member Joined: 19/03/2016 Location: AustraliaPosts: 129 |
Thanks Grogster. After Geoff's reply I wondered why such an important point was not in the manual. I opened it to search. Found it. It was there all the time! Just didn't see it. . . . L. - |
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| Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3308 |
Don't worry, there is a lot of stuff in the manual and when you first read it that part was probably not relevant. In part this is why TBS is such a great forum (thanks Glenn). Geoff Edited 2020-04-14 10:47 by Geoffg Geoff Graham - http://geoffg.net |
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