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+--- Thread: Serial port cable (/showthread.php?tid=9367)
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RE: Serial port cable - danielt - 03-12-2020
(03-11-2020, 03:37 PM)z4v4l Wrote:Quote:(IIRC 3.3v is, strictly speaking, slightly over-volted too... but hopefully it is within engineering tolerancesnot accordingly to the rk3399 datasheet, which claims 3.15 V as the acceptable maximum to that power domain.
I though that was the maximum for the power rail and the power rail is actually running at 3.0v (e.g. a 3.3v adapter will over-volt the RX pin by 0.3v, not 0.15v).
(when I bought my PBP I did also ordered some diodes with a forward drop of 0.3v and intended to use these to make hooking up an external programmer to the SPI FLASH strictly correct... however I'm not sure I can currently find them).
Edit:
Sorry, just realized I rather overlooked the obvious bit (I haven't looked the schematic for a while) which is that the engineering tolerance in the design doesn't come from the power rail anyway: it comes the 100 ohm resistors in series with TX and RX.
RE: Serial port cable - zaius - 03-13-2020
(03-11-2020, 02:41 PM)danielt Wrote: 3.3v adapters could cause touble (IIRC 3.3v is, strictly speaking, slightly over-volted too... but hopefully it is within engineering tolerances). However if they do cause trouble why are we not getting failure reports for that?
Maybe they using a different chipset?
"When serial interface output is free, the TXD in CH340H and CH340T is high level, TXD in CH340R is low-level."
https://cdn.sparkfun.com/datasheets/Dev/Arduino/Other/CH340DS1.PDF
RE: Serial port cable - danielt - 03-16-2020
(03-13-2020, 12:37 PM)zaius Wrote:(03-11-2020, 02:41 PM)danielt Wrote: 3.3v adapters could cause touble (IIRC 3.3v is, strictly speaking, slightly over-volted too... but hopefully it is within engineering tolerances). However if they do cause trouble why are we not getting failure reports for that?
Maybe they using a different chipset?
"When serial interface output is free, the TXD in CH340H and CH340T is high level, TXD in CH340R is low-level."
https://cdn.sparkfun.com/datasheets/Dev/Arduino/Other/CH340DS1.PDF
CH340R is a special case part designed to reduce part counts by eliminating the need for any external inverting buffer when interfacing with a system that does not idle at logic 1 (IrDA for example). Connecting this part to a device that does idle at logic 1 would make no sense and and when is doesn't work it would certainly not be due to any fault in the PBP.
RE: Serial port cable - zaius - 03-16-2020
(03-16-2020, 08:18 AM)danielt Wrote: CH340R is a special case part designed to reduce part counts by eliminating the need for any external inverting buffer when interfacing with a system that does not idle at logic 1 (IrDA for example). Connecting this part to a device that does idle at logic 1 would make no sense and and when is doesn't work it would certainly not be due to any fault in the PBP.
Selling a 5V adapter for computers with 3.3 inputs doesn't make sense either. I'm not suggesting that the problem is with the PBP. It's just from what I've read, the correct adapter should be both 3.3V and not hold the RX pin of the PBP while booting. The note on the NixOS Wiki doesn't specify whether the problem is from being held low or high.
RE: Serial port cable - xyzzy - 11-18-2020
It's common for chips to have reset strapping on some of their pins. Low strength pull-ups or pull-downs are used to set the pin high or low on reset and this is used to configured the chip in some way. Usually there are several for booting, e.g. which device(s) to try or what voltage the eMMC chip should use, etc. Then in normal use the pins are driven with enough power to counter the weak pulls from the reset strapping resistors.
So it could be the uart pin shouldn't be held the way the serial cable is holding it on reset, and this is misconfiguring the SoC.
Also the 3.0 V line that powers the IO pins in the uart block is probably not up instantly. There is usually a complex process with a PMIC that brings all the different power rails up on some order. So maybe uart RX is held at 3.3V externally and the Vcc supply for that pin is still at 0V. Bad things can happen in this case. That block might try to draw power through the RX IO pin since it's at a higher voltage than the supply pin.
I would have designed the board with a built in RS232-USB chip. The USB side is powered via the USB bus, so it does not disappear/reappear on the host device every time the PBP reboots or resets. This is really annoying. Minicom on Linux handles it admirably, and automatically re-connects quickly when the USB serial device reappears. Windows hyperterm is horrible and needs to be restarted. So you can never see the console from just after reset.
The RS-232 side of the chip is powered from the same 3.0V rail that powers the IO block in the RK3399 with the UART. That way the voltage is exactly correct! And it means the 232-USB chip will not power the IO pins before the RK3399 has power to those pins' block.
And then you could get the serial console with a simple micro usb cable. Wouldn't that be nice!
RE: Serial port cable - mattpenn - 03-03-2021
Hi all,
Is it still the case that the cable sold on the Pine store (https://pine64.com/product/pinebook-pinephone-pinetab-serial-console/?v=0446c16e2e66) is the incorrect voltage?
Ref: https://wiki.pine64.org/wiki/Pinebook_Pro#Using_the_UART
Quote:Please ensure that you are using a 3.3v interface (such as the CH340, FTDI-232R, or PL2303, which are sold in both 3.3v and 5v variants) to avoid damage to the CPU. The serial console cable sold by Pine64 uses wrong voltage level and should not be used; see this forum thread for further information.
Mine was delivered on Monday and I've yet to use it...
Thanks,
Matt
RE: Serial port cable - tllim - 03-04-2021
(03-03-2021, 08:32 AM)mattpenn Wrote: Hi all,
Is it still the case that the cable sold on the Pine store (https://pine64.com/product/pinebook-pinephone-pinetab-serial-console/?v=0446c16e2e66) is the incorrect voltage?
Ref: https://wiki.pine64.org/wiki/Pinebook_Pro#Using_the_UART
Quote:Please ensure that you are using a 3.3v interface (such as the CH340, FTDI-232R, or PL2303, which are sold in both 3.3v and 5v variants) to avoid damage to the CPU. The serial console cable sold by Pine64 uses wrong voltage level and should not be used; see this forum thread for further information.
Mine was delivered on Monday and I've yet to use it...
Thanks,
Matt
Should be correct 3.3V
RE: Serial port cable - mattpenn - 03-04-2021
Thanks for the update. I also confirmed with a multimeter and have removed that note about the Pine store version from the wiki.