Structure Of The Network Data Blocks (Ndb) - Siemens SIMATIC NET CP 243-1 Technical Manual

09/02
4.4.4

Structure of the Network Data Blocks (NDB)

The NDB is generated by the Ethernet Wizard in STEP 7 Micro/WIN 32. The
read/write commands possible for clients are configured in this data bock. Up to 32
read/write commands can be configured for each of the 8 possible communication
channels. If the CP 243-1 is operated on a channel as a server, then there is no
entry in the NDB structure for this channel.
The following table shows the structure of the NDB. The codes for read/write com-
mands are represented by the letters n, m, p = 0, ..., 31, and the channel codes are
represented by the letter r = 0, ...,7.
Byte offset in
variables memory
Header
128-129 NDB_LENGTH
Entries for first client channel
130 COM_CH0_ID
131 COM_CH0_OFF
132 COM_CH0_LEN0
...
n+132 COM_CH0_LENn
n+5 COM_CH0_0
... ...
+
n 5
COM_CH0_n
−
n 1
∑
+
COM _ CH 0 _ LENi
=
i 0
Entries for second client channel
... COM_CH1_ID
... COM_CH1_OFF
... COM_CH1_LEN0
... ...
... COM_CH1_LENm
... COM_CH1_0
... ...
... COM_CH1_m
... ...
Entries for n-th client channel
... COM_CHr_ID
CP 243-1
J31069-D0428-U001-A1-7618
Name
Specifies the length of the NDB
Code of first client channel
Specifies the offset to the first communication
block (COM0)
Specifies the length of the first communica-
tion blocks (COM0)
Specifies the length of the COMn structure
COM0 structure for read/write command 0 for
first client channel:
"<op>=<cnt>,<local_buffer>,<remote_buffer>"
(For description, see Table 6)
...
COMn structure for read/write command n for
first client channel:
"<op>=<cnt>,<local_buffer>,<remote_buffer>"
(For description, see Table 6)
Code of second client channel
(up to 8 channels)
Code of last client channel
Description
Configuration
Data
format
2 bytes hex
1 byte hex
1 byte hex
1 byte hex
n bytes
1 byte hex
ASCII
ASCII
ASCII
1 byte hex
1 byte hex
1 byte hex
1 byte hex
1 byte hex
ASCII
ASCII
ASCII
1 byte hex
43