Modbus RTU in Danfoss FC202 2

[Keith1976]

Hi All;

I am trying to read the relay status in Danfoss FC202 parameter 16-71. How can I do this? Using word status or 03HEX command?

I am a bit confused on the difference between STATUS WORD and reading DO status via 03HEX command? For example, if I want to know if there is alarm in the drive, should I define a DO as alarm and read the DO status? Or can I know the status via STATUS WORD?

The drives are used for chiller pumps in a building with Honeywell HC900 controller.

Thanks,
Keith

 

[Marke]

Hi Keith

You need to use 6 digit addressing, the address is 400000 + 16710 = 416710 ( the manual that I have suggests 40000 + 16710 = 56710 which is outside the range of many 5 digit drivers.
The alternative is to address using the offset method, but it depends on the capabilities of your controller.

Best regards,
Mark.

Mark Empson
L M Photonics Ltd

 

[ozmosis]

This attachment might help to understand better.

 

[Marke]

Hi Patrick

That assumes that the controller is able to use 5 digit addressing outside the range originally specified for 5 digit addressing. 40000 - 49999.
If the controller is able to operate outside this range, then you can use the 5 digit addressing. If the controller is not able, a driver written for the original standard, then either six digit addressing or offset addressing is required.

Best regards,

Mark Empson
L M Photonics Ltd

 

[ozmosis]

Good point Mark!

 

[Keith1976]

Marke;

Thanks for the reply.

According to Danfoss manual, I tried reading par 16-71 as follow:

1671 x 10 = 16710dec
16710 - 1 = 16709dec = 4145h

In Honeywell HC900 I switched the data type as "bit packed" and I can read the status of bit 3 and 4. The funny thing is that par 16-71 is supposed to be Unsigned integer 16

 

[Keith1976]

By the way Marke, when should I use Status Word (STW)? Is it more "accessible" than reading DO-status?

Rgds,
Keith

 

[Marke]

That depends on the controller that you are using.

I had problems with using the control word to start and stop an FC202, but no problems using alternative means. Still not sure if it was a PLC problem or a firmware issue.

Looks like you are able to use the function and offset with the offset unrestricted which is lucky!!

Best regards,

Mark Empson
L M Photonics Ltd

 

[danw2]

>In Honeywell HC900 I switched the data type as "bit packed" and I can read the status of bit 3 and 4. The funny thing is that par 16-71 is supposed to be Unsigned integer 16

It's quite common to bit pack a Modbus word and refer to it as unsigned integer format.

Unsigned integer 16 format tells you that
- the MSB is not sign bit, but a status or a null bit,
- it's a standard length, 16 bit, two byte word; not a float or a long value, hence it resides in a single slave register.

Dan

 

[Keith1976]

Thanks Dan