Applies To:
  • CitectSCADA 5.xx
  • CitectHMI 5.xx

I am getting S7NT driver error code 0x227A in the syslog.dat file. What does this error mean and how can I resolve this situation? 

0x227A is documented as GENERIC_GENERAL_ERROR, S7_ERR_MAX_REQ. This means the S7 API receives more requests than it can handle. See also Q3807, the Siemens Softnet S7 API has a limitation of a maximum of 2 simultaneous commands from a single external connection. There is not so much we can do about that scenario, other that decreasing the amount of physical request per second that the Citect application is generating. You could set the cache time to a higher value, use a higher page scan time, alarm scan time or slow down the trends by choosing a longer sample period.

Also a conflict between the S7NT timeout and the Softnet timeout could occur in some circumstances. Citect could make a retransmit while in Softnet the request has not timed out yet. To avoid that this disturbs communication a reasonable timeout for S7NT would be about 5 seconds with an S7NT card and about 15 seconds with a general TCPIP card. Retry should be set to 0 because the TCP network layer handles resends anyway.

So settings would be if you use a CP1613 card:


If you use a standard Ethernet card:


Another confirmed parameter combination that fixes this error is:

MaxPending = 1
Delay = 50
Timeout = 2000
Retry = 2

Note that this worked with v2.05.09.000A of the S7NT driver. Also, a persistant 'out of buffers usr.que' error was solved by setting the above parameters.