Zephyr Modbus RTU "Frame Error"

[RonVo]

Hello all,

I'm using the adafruit itsy bitsy for this modbus project and having issue to communicate with my usb-rs485 using modbus poll software. The protocol is Modbus RTU Slave and the error is <wrn> modbus_serial: Frame length error.

Any thoughts are appreciated!

here is my overlay file:

&uart0 {

    status = "okay";

    parity = "even";

    modbus0 {

        compatible = "zephyr,modbus-serial";

        status = "okay";

        //de-gpios = <&arduino_header 15 GPIO_ACTIVE_LOW>;  /* D9 */

    };

};

[Sigurd Hellesvik]

Hi,

For us to help you with this in the best possible way, please list the following information:

• SDK Version
• Which sample do you use, if any?
• Do you use custom code?
• What is the full log from the device?

 Regards,
Sigurd Hellesvik

[RonVo]

SDK Version: Zephyr version: 3.7.0-rc2
Full log of device:
[00:00:00.249,450] <inf> modbus_serial: RTU timeout 2005 us
[00:00:00.250,579] <wrn> modbus: Client wait-for-RX timeout
[00:00:00.250,579] <err> mbc_sample: FC16 failed with -116
[00:00:00.281,921] <wrn> modbus_serial: Frame length error
This is my code:

 */

#include <zephyr/kernel.h>

#include <zephyr/sys/util.h>

#include <zephyr/drivers/gpio.h>

#include <zephyr/modbus/modbus.h>

#include <zephyr/logging/log.h>

/* 1000 msec = 1 sec */

#define SLEEP_TIME_MS   1000

LOG_MODULE_REGISTER(mbc_sample, LOG_LEVEL_INF);

/* The devicetree node identifier for the "led0" alias.*/

static int client_iface;

const static struct modbus_iface_param client_param = {

    .mode = MODBUS_MODE_RTU,

    .rx_timeout = 1000,

    .serial = {

        .baud = 19200,

        .parity = UART_CFG_PARITY_EVEN,

        .stop_bits_client = UART_CFG_STOP_BITS_1,

    },  

};

#define MODBUS_NODE DT_COMPAT_GET_ANY_STATUS_OKAY(zephyr_modbus_serial)

static int init_modbus_client(void)

{

    const char iface_name[] = {DEVICE_DT_NAME(MODBUS_NODE)};

    client_iface = modbus_iface_get_by_name(iface_name);

    return modbus_init_client(client_iface, client_param);

}

int main(void)

{

    uint16_t holding_reg[8] = {'H', 'e', 'l', 'l', 'o'};

    const uint8_t coil_qty = 3;

    uint8_t coil[1] = {0};

    const int32_t sleep = 3000;

    static uint8_t node = 1;

    int err;

    uint8_t received[10];

    if (init_modbus_client()) {

        LOG_ERR("Modbus RTU client initialization failed");

        return 0;

    }

    err = modbus_write_holding_regs(client_iface, node, 0, holding_reg,

                    ARRAY_SIZE(holding_reg));

    if (err != 0) {

        LOG_ERR("FC16 failed with %d", err);

    }

}

[Sigurd Hellesvik]

I see that you get the error message "FC16 failed with -116". From errno.h this looks like EHOSTDOWN.
Try to check when modbus_write_holding_regs returns this error?

[RonVo]

I got it received the data now. However I'm not about to transmit. I connect the B- to Uart Tx but seem like it doesn't work that way. Is there any way I can transmit rs-485 without transceiver?

[Sigurd Hellesvik]

I don't have complete overview over this specific module I must admit. This means I will need some more context to be able to help.

RonVo said:

I got it received the data now.

What did you do to fix this?

RonVo said:

However I'm not about to transmit.

Any errors?