Siemens Simatic Operating Instructions Manual page 52

Functions
4.2 CAN transparent
Table 4- 10
Byte.Bit
0.7 ... 0.5
0.4 ... 0.1
0.0
1.7
1.6
1.5
1.4 ... 4.0
5-12
50
Structure of output data for transmit proxy modules (from S7 controller to PN/CAN LINK,
13 bytes)
Meaning
Reserved, must be "0"
Number of data bytes
Permitted values are 0 to 8. Values 9 to 15 result in the CAN message being discarded
and the "Last data faulty bit" to be set.
Send
When the bit changes to 1, the other data are applied and a corresponding CAN mes-
sage is entered in the transmit buffer. The PN/CAN LINK acknowledges receipt of the
transmit command by setting the transmit acknowledgment bit in the data for the
S7 controller to "1".
The S7 controller can then set the transmit bit to "0" and must wait until the PN/CAN
LINK has also set the transmit acknowledge bit to "0".
Only then can a new transmit command be issued.
Note: If the control bit is "0", the CAN messages are not entered in the transmit buffer but
are discarded instead.
Reserved, must be "0"
RTR flag
0 = Send normal data frame
1 = Send RTR frame
29/11-bit message ID
0 = 11-bit message ID
1 = 29-bit message ID
Message ID (in Big Endian)
For 11-bit message IDs byte 3 bit 2 is the most significant bit and byte 4 bit 0 is the least
significant bit. The remaining bits are ignored.
For 29-bit message IDs byte 1 bit 4 is the most significant bit and byte 4 bit 0 the least
significant bit.
Data bytes
In the order in which they are going to be sent
SIMATIC PN/CAN LINK
Operating Instructions, 03/2018, A5E39895388-AB