S7 300 analog output

Hello,
Could somebody tell me which FC or SFC on S7 300 PLC do I have to use to send a 4-20 mA signal through an analog ouput card?. In S5 115 PLC I have used the FB 251. Do I have to create my own FC or is there a FC in the S7 300 library ready to use?.
Thanks in advance,

Eduardo

Hola Sr. Pelegrin;
In the S7 world, you do not need a specific FC to write to an analog output; you can write directly to the PQW address.
Say you have a 4-20 mA output set at output address 512 (in Hardware Config). You can program a network anywhere in your program in which you MOVE (Load and Transfer in STL) a decimal value of 27648 to address PQW512 (peripherical output); this will output 20 mA on the appropriate connection. Any value between (decimal)5500 and 27648 will give you an output between 4 and 20 mA; any value above or below will result in an analog value error.
However, you can prefer to have Siemens do the scaling (eng. units to analog value) for your analog outputs: look at FC 106 "Uncale" in the TI-S7 conversion library on your Step 7 program editor. It is very simple to setup and very convenient.
Hope this helps,
Daniel Chartier

Dear all i am facing a problem with an AO4X12 bit. Actually it is connecting as the last element of a rack with an IM 153 and 4 other DI and DO cards. Wen i go online on the hardware configuration i get an x on this station only in this card and the message says that the current type of card is not available. Like network (profibus) can read it.Any suggestions?