Add RS485 mode support for UART2, UART3, UART4, and UART5. #6820
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6by9
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Apr 28, 2025
arch/arm/boot/dts/overlays/README
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| parameter, as RTS is required (default off). | ||
| rs485_invert_rts When RS485 mode is enabled, inverts the RTS | ||
| line from active-high (default) to active-low | ||
| (default off). |
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I'm not quite sure what you mean by "default off" here. You've already said the default is active-high. Applies to the other instances too.
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Thank you :) I meant that "rs485_invert_rts" is default off, but I appreciate that could cause confusion - would it be better if I just removed the last line of rs485_invert_rts on each instance?
Thank you - I've amended the potentially confusing documentation in a new commit. |
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kernel: Add driver for the Waveshare DSI-TOUCH series panels See: raspberrypi/linux#6566 kernel: Add support for TI ADS7828/ADS7830 I2C ADCs See: raspberrypi/linux#6819 kernel: Add RS485 mode support for UART2, UART3, UART4, and UART5 See: raspberrypi/linux#6820
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kernel: Add driver for the Waveshare DSI-TOUCH series panels See: raspberrypi/linux#6566 kernel: Add support for TI ADS7828/ADS7830 I2C ADCs See: raspberrypi/linux#6819 kernel: Add RS485 mode support for UART2, UART3, UART4, and UART5 See: raspberrypi/linux#6820
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This patch adds RS485 mode support for UART2/3/4/5.
This allows the RTS line to be used to drive the OE pin of an RS485 transceiver (i.e. MAX3078E).
I needed this for a project & it would be useful to have in-tree.
The "ctsrts" override is automatically activated, as this is required to enable the RTS line; there are also overrides to invert the RTS signal, and to set the RTS on and off delays to change the RTS timing around data transmission.
I haven't made changes to uart0-overlay.dts or uart1-overlay.dts as the syntax is quite different, I'm guessing this is legacy.
I also haven't made changes to uartX-pi5-overlay.dts as I'm unable to test these due to them being Pi5-only.
Tested and working OK on a CM4 with a pair of MAX3078E transceivers, overrides in /boot/firmware/config.txt as follows:
dtoverlay=uart3,rs485dtoverlay=uart4,rs485Credit to 6by9 for pretty much all of the device tree modifications here.
The associated forum thread is available here:
https://forums.raspberrypi.com/viewtopic.php?p=2311800