[FX30S] Rs485 directly (without Legato) remarks/questions


I used the Fx30S to perform serial communication through Rs485. I give you here somme comments and questions.

The thread “http://forum.legato.io/t/fx30s-rs485-port-cannot-set-termination-resistor-gpio-63/2600” from the Legato forum gave me some good information.

Description of my environment:

  • I am using a firmware built from the Yocto Legato-Dist-Source-mdm9x15-SWI9X15Y_07.11.21.00
  • I have not modified any driver related to the serial links

The manipulation:

  • I have configured the UART1 for the customer Linux application (AT!MAPUART=17), then rebooted the device
  • I have been using a program (written in C) to access the UART.

Here are my remarks / questions:

  • As said in the Legato forum, I confirm that the RS485 signal is on pins 1 and 2, and not on pins 1 and 3 as described in the user guide (rev 1).
  • I do not have the entry “/sys/devices/platform/msm_serial_hsl.0/rs_term”, nor “…/rs485_term” existing on my system. Why is that?
  • Is you driver totally compliant with TIOCSRS485? The call to “ioctl(ctx->s, TIOCSRS485, &rs485conf)” with “rs485conf.flags = SER_RS485_ENABLED” returns an error. I had to replace it with a write on “/sys/devices/platform/msm_serial_hsl.0/rs_mode”.

Best regards, Christian.

Hi Christian,

The firmware you’re using is for the stock WP85 module, which doesn’t have the RS485 driver.

Try loading the FX30 image from here:
source.sierrawireless.com/resou … -firmware/

R13.1.2.004 supports RS485 and you should see /dev/ttyHSL0 as well as rs_mode and rs485_term in /sys/devices…