Hi guys

I got a simple hardware setup 

1. CPU 1215C

2. CM 1241 Com module

3. DSE (Deepsea Electronics) 8610 genset controller

I'm trying to get some data over MODBUS using RS485 between the CPU and the genset controller. the problem is that some of the data like the KW readings are stored in two 16-bit registers, which both has to be read and then get combined together at the PLC to show the real value. Is this something possible to implement using the "1215C CPU".

Thanks in Advance

Hello,

something like this we have discussed here, maybe topic gives you some idea:

Issue getting floats from Modbus via 6ES7138-4DF11-0AB0

32 bit words that occupy two sequential 16 bit Modbus registers are typically one of two formats:

1) IEEE754 Floating point (also called "Real")

2) 32 bit long integers

The issue with either is interpreting the byte/word order at the application level in order to get the correct data value.

Modbus is not responsible for interpreting the data.   Modbus is only responsible for transferring the data.

To Modbus, it's only bits in registers, it neither knows nor cares whether it is encoded ASCII, a time stamp, a floating point value or an integer.  It's just binary bits.

The question that you need to investigate is

- what format is the data

- whether your hardware/firmware combination is capable of interpreting the bits back into a useful data value.

Hi AutoGen

The Data format is Floating Point Value. I am a bit of a beginner when it comes to the Modbus stuff, if someone could provide an software example of how this is done (Combining two 16bit regsiters to display one single data value 32bit), would be very helpful.

Thanks in advance

Hello marvin

32 bit data normally read/write by 2 sequential 16 bit words, you have to give length accordingly as per your read/write register are there.

if you are accessing 10 Nos of 32 bit real registers then you have to give pointer as below

P#DB1.DBX 0.0 Byte 40 (DB1 is for sample address only )

P#M10.0 byte 40 (M10 is for sample only)

one more thing during modbus data transfer some time received data may swap in words or bytes, mostly for 32 bit real/ floating addresses it may in words,

i.e. if you are reading address in DB1.DBD10 (32 bit real data address), this address we can split into

DB1.DBW10 & DB1.DBW12 (2- 16 Bits addresses) received data will swap in this word,

i,e 1st word will read in dbw12 & 2nd word in dbw10 & because of this 32 bit register value will differ than you actual device value, so please swap these words again then you will receive actual values which is displaying at your modbus source device.
swapping is not fixed as already autogen told you but my experienced swapping for 32 bit real registers are always in words as mentioned above.

if you want to get exact swapping then convert you source 32-register in binary format & also 2 sequential simatic 16 bit registers in binary format then you can find exact swapping format & also u will understand word/byte swapping.

in modbus address format 32 bit value will take 2 sequential registers 

i.e.---> 1st 32 bit holding 40001 

            2nd 32 bit holding 40003

likewise in simatic memory area 1st address will dependent on your pointer address which you have specify at pointer address, if it is DB1.DBW0 then your 

1st 32 bit holding register will be ---> 40001 ---->  DB1.DBD0

2nd 32 bit holding register will be----> 40003---> DB1.DBD4

& you can read above 32 bit real values by swapping your words as mentioned above in my reply.

if you need further clarification please contact again or unable to understood then also contact me again 

:-) hope u clear now