If it were me, I would suggest a low-end Siemens basic panel.  The time you will spend writing your custom HMI "driver" and integrating it with your project(s) may far exceed the cost of a Siemens basic panel of similar size.  Plus, the work getting the data to the HMI now falls to the HMI to request data it requires rather than creating custom writing routines to send data.

Oh, and it's RS232, so it's error prone, hence the CRC requirement.  Is there an acknowledgement response that the last data was received successfully, and an NOK (not ok)?

You can for sure do it, and perhaps this is one of those scrolling banner displays you want to send updates for production data to it?  Just curious.

As to solving the requested problem..

I would likely create helper FB, one for read and one for write, that accepts the various parameters of the message, then appends them together into an array of byte, or array of word depending on what the device's native data size is.  Most rs232 devices are byte-oriented, so probably array[0..n] of byte.

That array would then consist of the following (on the output of the read FB):

FB_read_232(addr[0] := 16#0F, addr[1] := 16#3E, value[0] := 16#FF, value[1] := 16#F0);

It then creates an array with the following values:

[ 16#5A, 16#A5, 16#01, 16#83, 16#0F, 16#3E, 16#FF, 16#F0, CRC16(16#5AA501830F3EFFF0) ]

If that FB_read_232 successfully creates the output array, you can then enable the rs232 send and point to the array / data buffer, and pass the length of the message = 10 to the send instruction block.

The F1-help should get you there.

If you do not know how to compute the CRC (16-bit), you can find the algorithm online in many locations, and if you search these forums, you hopefully find it in SCL so you can create a CRC-16 FB/FC to compute it for you as required for both reading and writing and only have one block that computes the crc (instead of putting that in both the read and write FBs.

Arasan

Dear Experts,

                             Am using S7-1200 plc and Cm1241 rs-232 Communication module .

Here i want to Communicate 3rd party HMI (DGUS).

That HMI Communication data write format Userdefined .

First we want to send Header - 5A A5

and Data length - (1 Byte)

And Commend - Write (82) read(83)

Data - Address(2 Byte)+ data value(2 byte)

And CRC check Sum value - 2 Byte.

Like this i want to transfer the datas.

it can be possible for our PLC Side . User difined data structure format we can able use it.??

kindly support this .

Thanks in advance,

Regards,

Arasan..