Technical data

Table Of Contents
Generating Block-Related Messages
System Software for S7-300/400 System and Standard Functions - Volume 2/2
24-4
A5E00739858-01
Amount of Transferable Data
The data transferred with the associated values SD_i of the NOTIFY, NOTIFY_8P,
ALARM and ALARM_8P SFBs must not exceed a maximum length. The maximum
data length is calculated as follows:
maxleng = min (pdu_local, pdu_remote) - diff - 4 * number of SD_i parameters
used
Where:
min (pdu_lokal, pdu_remote) is the lowest value of the data fields pdu_lokal und
pdu_remote
pdu_local is the maximum length of the data fields of the local CPU (see the
technical data of your CPU)
pdu_remote is the maximum length of data fields of the display devices
diff = 48, if acknowledgement triggered reporting is enabled, while diff = 44 if
disabled.
Example:
A CPU 414-2 is sending messages across Industrial Ethernet to WinCC.
Acknowledgement triggered reporting is disabled.
The associated values SD_1, SD_2 and SD_3 are used.
pdu_local = 480 bytes, pdu_remote = 480 bytes
Number of SD_i parameters used: 3
So that:
maxleng = min (480, 480) - 44 - 4 * 3 = 480 - 44 - 12 = 424
The maximum length of data that can be transferred per SFB is 424 bytes.
See also:
Configuring Messages