Siemens Simatic Operating Instructions Manual page 54

Functions
4.2 CAN transparent
In the input data from the PN/CAN LINK to the S7 controller, the PN/CAN LINK transmits
received CAN messages and information on whether there was a receive buffer overflow.
Such an overflow occurs when too many CAN messages with matching message ID were
received before they could be transmitted to the S7 controller.
Note
The order of the data bytes in the received CAN messages is not changed in the PN/CAN
LINK. Any necessary adaptation to compensate for "endianness" must be made in the
S7 user program.
Note
For values made up of multiple bits, the first bit is the MSB and the last bit is the LSB.
Example: Byte.Bit 3.0 ... 4.6 = 2 means that byte 3 bit 0 = "0", byte 4 bit 7 = "1" and
byte 4 bit 6 = "0".
Table 4- 12
Byte.Bit
0.7
0.6
0.5 ... 0.1
0.0
52
Structure of output data for receive proxy modules
(from S7 controller to PN/CAN LINK, 1 byte)
Meaning
Receive buffer
0 = No action
1 = All CAN messages in the receive buffer are deleted
Receive filter
0 = Only received CAN messages that match the receive filter are entered in the receive
buffer and later forwarded to the S7 controller
1 = All received CAN messages are entered in the receive buffer and later forwarded to
the S7 controller
Reserved, must be "0"
Receive enable
If the bit has the value 1 and the PN/CAN LINK has a CAN message in the receive buffer
of the receive proxy, the PN/CAN LINK enters the message in the data for the S7 con-
troller and sets the "Message exists" bit to "1".
The S7 controller must then set the receive enable bit to "0" and must wait until the
PN/CAN LINK has also set the "Message exists" bit to "0".
Only then may the S7 controller set the receive enable bit to "1" again.
SIMATIC PN/CAN LINK
Operating Instructions, 03/2018, A5E39895388-AB