Pull-down on UART CTS pin

Technical Support
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1

Verdin Mini Q 2GB, custom yocto build from latest Toradex BSP, custom carrier board

Is it possible to make device tree change or device tree overlay to activate pull down resistor on UART1 CTS pin (sodimm pin 135)?

Purpose is to allow linux to transmit on UART1 with RTSCTS HW handshaking enabled even if pin 135 (CTS) has no connection. Without the change, pin is either floating or pulled up and this blocks Transmit function on this UART.

Thanks
Branislav

2

Hi @bbezak , according to the chapter 8.2.5.267 of iMX8MMini RM, the bit 6 is for Control IO ports PS. 0->Select pull-down resistors, 1->Select pull-up resistors. Our default device tree sets MX8MM_IOMUXC_SAI3_RXD_UART2_DCE_RTS_B to 0x1c4. To enable a pull-down resistor, you can set it to 0x184.

3

Hi Benjamin,
this is great! We would like to apply this in our yocto recipe, what is the easiest way how to do it?
Thanks
b.

4

I think the device tree needs to be recompiled and deployed. You can copy the binary dtb file to /boot on the device and replace the one that exists. This is how to download and compile source code.

5

This worked! Thanks for your help. You can close this issue.