Echelon IzoT U60 DIN, User Manual

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IzoT U60 DIN Network Interface User’s Guide
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5
CpMsgReject
An attempt to transfer a message downlink
is rejected because of a lack of buffer
space.
This code packet will be a response to a
downlink
CpMsgReq code packet or a
response to a CpMsg without the
CpMsgReq being sent.
This code indicates that the offered
downlink traffic is more than the U60 can
handle (it has no more APP or NET output
buffers).
Upon receiving this code, the device driver
should repeat the message send process
until it succeeds.
U
6
CpNiCmdShort
Sends a single byte local network interface
command. The command is stored in the
Param Data field.
U/D
7
CpResync This command is sent by the host to start
a new session with the U60. When
received it will reset the transmit and
receive sequence numbers to zero so that
any subsequent sequence numbers will
be accepted rather than rejected.
This command is also a good way to
establish that communications are
functioning with the U60.
The U60 always responds to this
command with a
CpNull packet, so the
host can determine that the serial link is
not simply echoing data.
D
Notes :
•
Use symmetrical timeouts on the host processor. There is an inter-byte timeout
on the client side of 40ms when receiving either a code packet or a message
body. There is a timeout of 250ms when waiting for the start of a downlink
message CpMsg following a CpMsgReq / CpMsgAck sequence.
• All length fields do not count for escape prefixes. Instead, they reflect the
length of the real data stream above the link-layer protocol. All length fields
do not account for the checksum.
• Broken code packets (code packets with missing or corrupt bytes) are not
responded to at all, and they rely on time-out mechanisms for re-
transmission.
• Broken message streams are responded to as soon as the error condition
is observed. The response is the CpFail code packet.