using asynchronously operating SFC84

[MacGyver]

I intend to store recipe from linked DB in RAM to unlinked DB in MMC. This could be done with SFC84 and works. The only problem I have is that I don't know when writing is finished.



When I start writing with REQ=1, I get the signal BUSY=1. In first cycle RET_VAL is 7001 and later 7002 (at that point REQ=0). Then RET_VAL stays 7002 and busy stays 1 for ever.



Codes 7001 and 7002 mean:

7001 - First call with REQ=1: no data transfer active; BUSY has the value 1.
7002 - Intermediate call (REQ irrelevant): data transfer already active; BUSY has the value 1.



If I stop writing (stop calling SFC84) and check data in written DB, there are successfully stored data, but I don’t know when to stop writing (stop calling SFC84).



Has anyone worked with SFC84 or any other asynchronously operating SFC? Any idea?

 

[S7Guy]

I've worked with many of the SFCs, so maybe I can help.

What do you mean by this:

If I stop writing (stop calling SFC84) and check data in written DB, there are successfully stored data, but I don’t know when to stop writing (stop calling SFC84).

Normally, the SFCs need to be called continuously until the job is complete, even though they are "asynchronous". Is it possible that you are using the request bit to call SFC84, and when it goes low, SFC84 isn't called anymore? If so, that would cause it to get "stuck" with status 7002.

You should either unconditionally call SFC84, or use an intermediate bit that is set when the request goes high and is reset when the job is finished (Busy goes from 1 to 0).

If that isn't the problem, then we'll try to think of something else.