Experimental Physics and
Industrial Control System

Mark Rivers via Tech-talk <[email protected]> · Tue, 22 Oct 2019 10:51:33 +0000

Hi Vishnu,

> (2) With holding register(03) READ function is ok.
> But write gives an error as below
> 2019/10/22 15:11:41.117 drvModbusAsyn::doModbusIO port DACD_AMT_EU1_RW_MW_11000 error calling writeRead, error=, nwrite=6/6, nread=0
> iocRun: All initialization complete
> epics> 2019/10/22 15:12:20.517 drvModbusAsyn::writeUInt32D port DACD_AMT_EU1_RW_MW_11000 invalid request for Modbus function 3
> 2019/10/22 15:12:20.517 DACD_AMT_W_FR1 devAsynUInt32Digital::processCallbackOutput process error

The problem is that you are trying to use the same port for the read operation and the write operation, which is not correct.  The port was created with Modbus function 3 which is Read Holding Registers. You need to create a second port with Modbus function 6 which is "Write Single Register".  The longin record uses the port with function 3 and the longout record uses the port with function 6 (or 16).

> (1)I used  write function for "write multiple coils (15)" modbus function.
> drvModbusAsynConfigure("DACD_AMT_EU1_WRITE_MB_0000",  "DACD_AMT_EU1", 1, 15, 0, 32,    0,  100, "EU")
> The function error output below.
> 2019/10/22 14:58:49.789 drvModbusAsyn::doModbusIO port DACD_AMT_EU1_WRITE_MB_0000 error calling writeRead, error=, nwrite=6/6, nread=0

First, have you checked that the device supports function code 15?  The manual should tell you what function codes are supported.

Second, this error
> 2019/10/22 14:58:49.789 drvModbusAsyn::doModbusIO port DACD_AMT_EU1_WRITE_MB_0000 error calling writeRead, error=, nwrite=6/6, nread=0

is not what I expect if the device does not support the operation or if you are using an invalid address etc.  The above error says that the device did not send any response at all.  What it should do is to send an error code.

You said the device is RTU.  With RTU you need to set a delay before each write to the device with the writeDelayMsec argument to modbusInterposeConfig:

modbusInterposeConfig(portName,
                      linkType,
                      timeoutMsec,
                      writeDelayMsec)

Did you do that?  Is your device serial, and if so what baud rate?

You can enable ASYN_TRACEIO_DRIVER in the underlying serial port or TCP driver to see all of the messages sent and received.

Mark

________________________________
From: Tech-talk <[email protected]> on behalf of Vishnu Patel via Tech-talk <[email protected]>
Sent: Tuesday, October 22, 2019 4:47 AM
To: [email protected]
Subject: modbus Write operation

Hi,

   I would like to write using modbusRTU EPICS Driver.

(1)I used  write function for "write multiple coils (15)" modbus function.

drvModbusAsynConfigure("DACD_AMT_EU1_WRITE_MB_0000",  "DACD_AMT_EU1", 1, 15, 0, 32,    0,  100, "EU")

The function error output below.

2019/10/22 14:58:49.789 drvModbusAsyn::doModbusIO port DACD_AMT_EU1_WRITE_MB_0000 error calling writeRead, error=, nwrite=6/6, nread=0

(2) With holding register(03) READ function is ok.

But write gives an error as below

2019/10/22 15:11:41.117 drvModbusAsyn::doModbusIO port DACD_AMT_EU1_RW_MW_11000 error calling writeRead, error=, nwrite=6/6, nread=0
iocRun: All initialization complete
epics> 2019/10/22 15:12:20.517 drvModbusAsyn::writeUInt32D port DACD_AMT_EU1_RW_MW_11000 invalid request for Modbus function 3
2019/10/22 15:12:20.517 DACD_AMT_W_FR1 devAsynUInt32Digital::processCallbackOutput process error

I am reading and write Holding Register 11000 using longin & longout record.

file "../../db/longin.template" { pattern
{P,           R,                PORT,     OFFSET,   SCAN}
{DACD_AMT_,     R_FR1,          DACD_AMT_EU1_RW_MW_11000,       0,     "I/O Intr"}
}

file "../../db/longout.template" { pattern
{P,           R,               PORT,      OFFSET}
{DACD_AMT_,     W_FR1,          DACD_AMT_EU1_RW_MW_11000,    0}

I am not able to write "multiple coils" function and "write holding register" .

Thanks
Vishnu

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System