Siemens Local_tsap_id

[DLMUK]

Hi,

On a modbus block for an S7-314 I need to set the parameter local_tsap_id and have the following description in the manual...

This parameter defines the local port number.

local_tsap_id[1] high byte of the local port number in hexadecimal
local_tsap_id[1] low byte of the local port number in hexadecimal
local_tsap_id[3-16] B#16#00

I understand the port number needs to be 2000. What I don't know is what to put in the high byte, low by fields.

I have my low byte as D0 and high byte as 7 in hex. Does this make sense?

my logic is...

low byte = 1101 0000 = D0 in hex
high byte = 0000 0111 = 7 in hex

Thanks

 

[mk42]

Hi,

On a modbus block for an S7-314 I need to set the parameter local_tsap_id and have the following description in the manual...

This parameter defines the local port number.

local_tsap_id[1] high byte of the local port number in hexadecimal
local_tsap_id[1] low byte of the local port number in hexadecimal
local_tsap_id[3-16] B#16#00

I understand the port number needs to be 2000. What I don't know is what to put in the high byte, low by fields.

I have my low byte as D0 and high byte as 7 in hex. Does this make sense?

my logic is...

low byte = 1101 0000 = D0 in hex
high byte = 0000 0111 = 7 in hex

Thanks

What you did sounds right to me, but byte order/endianness issues are sometimes more complicated than they seem like they should be.

To be honest, I find the best way is to guess (like you did) then try it and see if it works. If it doesn't, flip it and see if it works the other way.

 

[DLMUK]

FYI

spoke to Siemens tech support and I had it the wrong way.

Low byte = 07 and high byte = D0