Data Exchange - WAGO -I/O-SYSTEM 750 Manual

78 Appendix
10.1.3.2

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
Bit 3
1
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.
Bit 2 Bit 1 Bit 0
T 0x00
Control Nibble
Bit 3 Bit 2 Bit 1
1 T 0x00
Version 1.2.0, valid from FW/HW-Version 01/01
WAGO-I/O-SYSTEM 750
750-658 CAN Gateway
Bit 0
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