ESP32 Forum

Posted: **Tue Jan 10, 2023 5:20 pm**

Hi,

I'm having issues with defining multiple separate Modbus holding register areas using the serial slave example. I get the following error:
"MB_CONTROLLER_SLAVE: mbc_slave_set_descriptor(217): mb incorrect descriptor or already defined."

Here is how I define the areas in the main app:

Code: [Select all] [Expand/Collapse]

#define MB_REG_HOLDING_START_AREA0          (40263)
#define MB_REG_HOLDING_START_AREA1          (40267)
#define MB_REG_HOLDING_START_AREA2          (40291)
#define MB_REG_HOLDING_START_AREA3          (40293)
#define MB_REG_HOLDING_START_AREA4          (40389)
#define MB_REG_HOLDING_START_AREA5          (40907)
#define MB_REG_HOLDING_START_AREA6          (40931)
#define MB_REG_HOLDING_START_AREA7          (40933)
#define MB_REG_HOLDING_START_AREA8          (41027)
 
static void setup_reg_data(void)
{
    // Define initial state of parameters
    holding_reg_params.reg263= 0;
 
    holding_reg_params.reg267 = 0;
 
    holding_reg_params.reg291 = 0;
 
    holding_reg_params.reg293 = 0;
 
    holding_reg_params.reg389 = 0;
 
    holding_reg_params.reg907 = 0;
 
    holding_reg_params.reg931 = 0;
 
    holding_reg_params.reg1027 = 0;
}
 
    reg_area.type = MB_PARAM_HOLDING; // Set type of register area
    reg_area.start_offset = MB_REG_HOLDING_START_AREA0; 
    reg_area.address = (void*)&holding_reg_params.reg263; 
    reg_area.size = sizeof(float) << 1;
    ESP_ERROR_CHECK(mbc_slave_set_descriptor(reg_area));
    reg_area.type = MB_PARAM_HOLDING; // Set type of register area
    reg_area.start_offset = MB_REG_HOLDING_START_AREA1; 
    reg_area.address = (void*)&holding_reg_params.reg267; 
    reg_area.size = sizeof(float) << 1;
    ESP_ERROR_CHECK(mbc_slave_set_descriptor(reg_area));
    reg_area.type = MB_PARAM_HOLDING; 
    reg_area.start_offset = MB_REG_HOLDING_START_AREA2; 
    reg_area.address = (void*)&holding_reg_params.reg291; 
    reg_area.size = sizeof(float) << 1; 
    ESP_ERROR_CHECK(mbc_slave_set_descriptor(reg_area));
    reg_area.type = MB_PARAM_HOLDING; 
    reg_area.start_offset = MB_REG_HOLDI    NG_START_AREA3;
    reg_area.address = (void*)&holding_reg_params.reg293; 
    reg_area.size = sizeof(float) << 1; 
    ESP_ERROR_CHECK(mbc_slave_set_descriptor(reg_area));
     reg_area.type = MB_PARAM_HOLDING; 
    reg_area.start_offset = MB_REG_HOLDING_START_AREA4;
    reg_area.address = (void*)&holding_reg_params.reg389; 
    reg_area.size = sizeof(float) << 1; 
    ESP_ERROR_CHECK(mbc_slave_set_descriptor(reg_area));
    reg_area.type = MB_PARAM_HOLDING; 
    reg_area.start_offset = MB_REG_HOLDING_START_AREA5;
    reg_area.address = (void*)&holding_reg_params.reg907; 
    reg_area.size = sizeof(float) << 1; 
    ESP_ERROR_CHECK(mbc_slave_set_descriptor(reg_area));
    reg_area.type = MB_PARAM_HOLDING; 
    reg_area.start_offset = MB_REG_HOLDING_START_AREA6; 
    reg_area.address = (void*)&holding_reg_params.reg931; 
    reg_area.size = sizeof(float) << 1; 
    ESP_ERROR_CHECK(mbc_slave_set_descriptor(reg_area));
    reg_area.type = MB_PARAM_HOLDING;
    reg_area.start_offset = MB_REG_HOLDING_START_AREA7;
    reg_area.address = (void*)&holding_reg_params.reg933;
    reg_area.size = sizeof(float) << 1; 
    ESP_ERROR_CHECK(mbc_slave_set_descriptor(reg_area));
    reg_area.type = MB_PARAM_HOLDING; 
    reg_area.start_offset = MB_REG_HOLDING_START_AREA8; 
    reg_area.address = (void*)&holding_reg_params.reg1027; 
    reg_area.size = sizeof(float) << 1; 
    ESP_ERROR_CHECK(mbc_slave_set_descriptor(reg_area));
    reg_area.type = MB_PARAM_HOLDING; 
 
 
    setup_reg_data(); // Set values into known state

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What am I doing wrong? It specifically complains on the reg293 reg_area, so it's okay with the first 3. Each register in the program is just a single float register in my definition.

Thank you in advance!

Posted: **Thu Jan 12, 2023 10:49 am**

Hi @Nikostpn,

Unfortunately you define the areas incorrectly. Actually I do not see the structure holding_reg_params and my guess about your structure may be incorrect. Please provide the holding_reg_params structure for more information.

Code: Select all

    reg_area.type = MB_PARAM_HOLDING; // Set type of register area
    reg_area.start_offset = MB_REG_HOLDING_START_AREA0;
    reg_area.address = (void*)&holding_reg_params.reg263;
    reg_area.size = sizeof(float) << 1;
    // This call registers the register area in the memory from &holding_reg_params.reg263 with length = 4 (sizeof float) * 2 (registers 263, 264, 265, 266) = 8 bytes!. So, the &holding_reg_params.reg267 corresponds to registers 265, 266 in this area.
    ESP_ERROR_CHECK(mbc_slave_set_descriptor(reg_area));
    reg_area.type = MB_PARAM_HOLDING; // Set type of register area
    reg_area.start_offset = MB_REG_HOLDING_START_AREA1;
    reg_area.address = (void*)&holding_reg_params.reg267;
    reg_area.size = sizeof(float) << 1;
    // Here you starting to register the new area starting from memory address &holding_reg_params.reg267, but its already registered in previous area. This causes the error!

You can define the first register area with length

Code: Select all

        reg_area.address = (void*)&holding_reg_params.reg263;
	reg_area.size = sizeof(float); // 4 bytes in the memory starting from &holding_reg_params.reg263

, or just add :

Code: Select all

    holding_reg_params.reg263 = 0;
 	      holding_reg_params.reg265 = 0; // add the field to keep registers 265, 266 into your holding_reg_params structure (uint16_t).
    holding_reg_params.reg267 = 0;

Also please note that the modbus registers in the esp-modbus defined as zero based. So, the PLC holding register 40263 is defined as 263 :

#define MB_REG_HOLDING_START_AREA0 263

Please refer to https://docs.espressif.com/projects/esp ... ata-access, for more information on how to configure the register areas in the modbus slave.

Posted: **Tue Jan 17, 2023 4:02 pm**

Hi ESP_alisitsyn,

Thank you for your answer! I was able to resolve this. My issues were that I was linking the wrong modbus_params.h file -- since I went off the serial slave example, the esp-modbus stuff was automatically copied over as a component into my project once I started changing it, but the CMakeLists.txt file was still linking the component that was in my esp-idf; and yes, I was incorrectly defining the Modbus register areas ('4xxxx' instead of just 'xxxx'). I didn't see your message until now so I was changing the register areas until they worked, but possibly a more verbose example in the docs would do good.

Posted: **Wed Jan 18, 2023 10:40 am**

Hi Nikostpn,

It is good that the issue is solved.

I didn't see your message until now so I was changing the register areas until they worked, but possibly a more verbose example in the docs would do good.

I will think about verbose example in the updated documentation to make it clearer.

ESP32 Forum

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