Re: autoConnect could not connect when reading a register by modbus relative addressing

[Mark Rivers via Tech-talk <tech-talk at aps.anl.gov>]

I think I see the problem.


  *
drvModbusAsynConfigure("DM2C_1_1_In_Word", "L0", 1, 3, 24576, 2, 0, 0, "DM2C_stepper")

That creates a driver that will use function code 3 to read from register location  24576 (0x6000).  It will read 2 registers (the Modbus length argument), so it will read registers 0x6000 and 0x6001.


  *   status = pC_->readReg16(44, &read_val, DEFAULT_CONTROLLER_TIMEOUT);

However, here you are telling it to read relative register 44 (0x2c) which is absolute register 0x602c. That is invalid because you only configured the driver to read 2 registers.  You need to increase the number of registers in the drvModbusAsynConfigure to include all registers you will be accessing.

Mark



________________________________
From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of 沈治邦 via Tech-talk <tech-talk at aps.anl.gov>
Sent: Friday, November 22, 2024 4:31 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: autoConnect could not connect when reading a register by modbus relative addressing


Hi,


I am encountering an issue while developing a modbus communication-based motor controller program, similar to the module motorAMCI.


I am attempting to read the values in registers with function code 3 by relative address. For instance, if I want to read the value located in 0x602C, which represents the current position of the motor. I set the starting address to 0x6000 by the command in st.cmd


drvModbusAsynConfigure("DM2C_1_1_In_Word", "L0", 1, 3, 24576, 2, 0, 0, "DM2C_stepper")


Then to read the motor position, I called the function in driver.cpp with sentence


status = pC_->readReg16(44, &read_val, DEFAULT_CONTROLLER_TIMEOUT);


24657 is 0x6000 and 44 is 0x2C, then I believe that the value at 0x602c could be accessed.


The definition of the readReg16 is the same with the method ANG1Controller::readReg16()


Consequently, I am unable to retrieve the correct register value, and an error is showed:


2024/11/22 17:57:00.751 DM2C_1_1_In_Word 2 autoConnect could not connect:


Could someone please help me figure out what might be causing this issue?


Thank you!



Best regards,

Shen Zhibang