Hi Friends,

I am implementing the Diagnostic function (08) for sub-function code 00 01. what is "Continue on Error" and "Stop on Error" mode in Modbus.

Thank you,
Prasanth M V
prasanthmv [at] ushustech.com

 

Function Code 8 is an obsolete command created exclusively for the Modicon 484 PLC product back in 1978. It has NEVER been a generally used command in 3rd party Modbus devices and is almost never supported in current host products (i.e. no host will send this command to your device).

The closest "Replacement" is Function Code 17 created in 1980 (Report Slave ID) supported by Modicon 584/984 Controllers however very few 3rd party devices support this command and a limited number of host products. The purpose in the case of Function Code 8 & 17 has been to provide a means of getting the basic configuration of a device along with the operation state (running, idle) and even battery status.

What is it that you are trying to create that you are implementing this function code?

Generally speaking it is easier to reserve a block of 4XXXXX registers that will contain system ID, Vendor etc in a contiguous information block, and have the host read this using function code 4.

In general a smart sensor, microcontroller etc can be entirely implemented using no more then 4 Modbus Commands -
Read Coil (code 01)
Read 4XXXXX (code 03)
Write Coil(s) (code 15)
Write 4xxxxx(s) (code 16)

Don't waste your time getting too fancy - concentrate on the quality of information your device can supply:
a.) Vendor Name (typically up to 32 x 4xxxx)
b.) Product Name (typically up to 32 x 4xxxx)
c.) Product Part #(typically up to 32 x 4xxxx)
d.) Product Serial #(typically up to 16 x 4xxxx)
e.) Range of 0XXXXX, 4XXXXX supported

Other nice features to store in 4xxxxx and allow the user to write to are:
a.) Date of Installation
b.) Date of FAT
c.) Date placed in service
d.) User Designation(s) for device like name, ISA Tag, Asset Tag, physical location

 

OK. Thanks for the information.
I accept what you said on Diagnostics function.

Anyway please let me know what is meant by "Continue on Error" and "Stop on Error" in modbus.

Thanks,
Prasanth M V
Sofware Engineer
Ushus Technologies.

 

I think "Continue on Error" is when you have any error communication on your Modbus, then the communication will neglect any error and still transmit the data, the good one still update on your HMI, the bad one will not update the value. But for "Stop on Error" is when you have any error during transmit Modbus data, then Modbus communcation will stop the transfer and you will not get any data in your modbus. in modbus. you can program this status with alarm to show when this status will raise.

See your programming manual for this matter.