RE: A question on modbus

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

Hi Kevin,

 

• There is another command to open the device, which should write " \x01 \x05 \x00 \x00 \xFF \x00  \x8C \x3A" to the device.

 

That is a standard Modbus command.  It uses function code 5 (write single coil) using data="" to address=0.  The value 0xff00 is what the Modbus standard requires to be written to a single coil for the bit value 1.

You need to create another driver with this command:

 

drvModbusAsynConfigure("V1","Init", 1,5,0,1,0,0, "Init")

 

You can create a template file called modbusInit.template in the same directory with your startup script.

 

record(bo,"$(P)$(R)") {

    field(DTYP,"asynUInt32Digital")

    field(OUT,"@asynMask($(PORT) 0 0x1)")

    field(VAL, “1”)

    field(PINI, “YES”)

}

 

That record will process during iocInit (because PINI=YES).  It will write the value 0xff00 to address 0 using function code 5.

 

Load that file in your startup script with the command

 

dbLoadRecords(modbusInit.template”, “P=power:,R=init,PORT=V1”)

 

Mark

 

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Amber via Tech-talk
Sent: Tuesday, July 11, 2023 3:04 AM
To: tech-talk <tech-talk at aps.anl.gov>
Subject: A question on modbus

 

Hello everyone，

 

I am using a device with Modbus-RTU protocol. The communication data is transmitted in hexadecimal words.

I want to use the modbus module in epics to solve this problelm. 

 

When reading device data, the follwing sentence is used in the .cmd file:

 

drvModbusAsynConfigure("V1","Power", 1,3,0,1,0,1000, "Power")

 

and in the substitution file:

 

file "../../db/ai.template" { pattern

{P,         R,      PORT,               OFFSET, BITS,  EGUL,  EGUF,   PREC,   SCAN}

{power:,    V_read,   V1,   0,      16,    0.,   655.35,     2,      "I/O Intr"}

}

 

There is another command to open the device, which should write " \x01 \x05 \x00 \x00 \xFF \x00  \x8C \x3A" to the device.

Command	01	05	00	00	FF	00	8C	3A
	Address	Function code	Register address 0		Data 0		CRC
Reply	Be same with command

 

After reading all the examples I still don't know how to send this command with modbus module correctly. I think I didn't understand them clearly.

Would you like to give me some advice?  Is it suitable to use modbus module?  How to realize it?

Thank you very much.

 

with my best wishes,

Kevin