90 Appendix
WAGO-I/O-SYSTEM 750
750-658 CAN Gateway
Manual
Version 1.2.1, valid from FW/HW-Version 01/01
12.1.3.2 Data Exchange
In the data exchange phase, the handshake byte is used in Toggle mode.
Because a message is normally larger than the data part of the transmission
channel, the message must be transferred in several cycles (fragmentation).
Status Nibble
Control Nibble
Bit 3 Bit 2 Bit 1 Bit 0
Bit 3 Bit 2 Bit 1 Bit 0
1
T
0x00
1
T
0x00
Send fragment:
The first toggle bit expected by the receiver after synchronization has the value 0.
The toggle bit in the second fragment receives a 1, the toggle bit in the third
fragment again a 0, etc. Only when the status of the toggle bit matches in the
received status nibble is receipt of the fragment confirmed by the receiver. Only
then can a new fragment be sent. As long as there is no confirmation, the
fragment remains unchanged in the process image.
For the special case that the content of the send buffer is no longer sufficient to
fill the transmission channel completely, the transmission channel is filled with
zeros to the end.
Receive fragment:
The control now has to confirm receipt of this fragment. Receipt is confirmed by
inverting the toggle bit of the status nibble to be sent.
Because the Mailbox 2.0 mechanism is full-duplex capable, data can be sent and
received at the same time.