SFC14 + 15 In Function Block Question

Hi again

I am currently ready inputs through SFC14 and then I am using the DB nr as input to a FB. Within the FB I use indirect addressing to access the DB Values.
When I am done with the FB I use the DB manipulated values as outputs using SFC15.

Now my question is can I use indirect address to write a value like this: P#DB27.DBX0.0 BYTE 14 which is the 'RECORD' any value using just the '27' DB value? Thus would reduce my program somewhat.

I hope my question makes sense

hein123 said:

Now my question is can I use indirect address to write a value like this: P#DB27.DBX0.0 BYTE 14 which is the 'RECORD' any value using just the '27' DB value?

Click to expand...

I cannot understand the question. Could you please elaborate? Example?

Kalle

Sounds like your making life way more complicated than it really needs to be, especially if you only have 14 bytes of I/O.

In the bad old days, PLC i/O was directly addressed so people made their own process images in data blocks so they could ensure that the I/O state remained contstant for an entire scan. Most modern PLCs, have a built in process image so that you don't need to make your own but some people still think it's a good idea. There can be legitimate reasons for doing this but generally, the term Ludite springs to mind.

Nick

P.S. sorry if i'm rambling a bit, it was a very nice bottle of wine.

I am actually writing to a rexroth servo motor and want to send all the information via SFC14 0 inputs and SFC15 - outputs.

For controlling the servo I have 3 Network Rows, one for ready the inputs, one with a FB for the control of the servo and then the I write to the outputs via SFC15.
What I basically do inside the FB is manupulate the Inputs and control outputs, but I do this by reading / writing to DB values. As inputs to the FB I have the numbers of the Input DB and the Output DB. I then use these numbers via indirect addressing to access the DB values:

L #S_InputDB_NR //Input DB Nr
T #iDB //Temp Holder
OPN DB [#iDB]
L 0
SLD 3
LAR1

A DBX [AR1,P#0.0] // Write Values To STAT
= #Q_OperationMode0
etc ...

Click to expand...

The FB works right so I am not worried about operation, but I would like to control the drive within one FB which would make future projects a bit easier.

SFC14:

CALL "DPRD_DAT"
LADDR :=W#16#B4
RET_VAL:=MW62
RECORD :=P#DB27.DBX0.0 BYTE 14

Click to expand...

Now what I want to do is place SFC14 code (ABOVE) on top of the FB. But the 27 of the P#DB27.DBX0.0 BYTE 14 needs to be an input as I won't always use DB27 as the Inputs DB. I want to access it via indirect addressing if possible like in the code above.

I know I can write to the outputs directly, however a tech working at Siemens told me it's better practice to use SFC14 and 15.


I hope this makes my question more clear

Call the following FC instead of SFC14

Thanks a lot it is working

I'm glad you got it working. In future you may wish to considder putting your drive data into two UDTs, one for READ and one for WRITE. You can then pass a pointer to your UDTs into the FC which can be deconstructed and used to build anypointers for SFC14/15. In this way, if you change the size of the data that is transferred, simply update your UDTs, do a block Consistency Check and thats it - job done.

Nick