Echelon IzoT U60 DIN, Руководство пользователя

Страница: 25 / 34

IzoT U60 DIN Network Interface User’s Guide
23
Type Code Values
The following table lists the values for the Type Code byte. Uplink means that data
is transferred from the U60 to the host processor. Downlink means that data is
transferred from the host processor to the U60.
Value Type Description
Uplink /
Downlink
0 CpNull
No data is being sent. Use this value for
acknowledge-only packets, or for pinging.
U/D
1 CpFail
The previous transfer was broken or in
error. This is typically due to checksum
errors or fragmented transfers. The
correct response to this command is to
resend the previous transfer.
U/D
2 CpMsg One message follows. A message is any
multi-byte network interface transfer and
requires an application output buffer or
packet buffer in the downlink case. The
number of messages is stored in the
Param Data field.
This value is limited to one in both the
downlink and uplink case.
The message follows the code packet
checksum byte, and consists of a length
byte, the NI command, the message itself,
and a checksum.
U/D
3 CpMsgReq Optional. Sent by the host for requesting
both the attention of the U60 and
requesting an uplink
CpMsgAck .
The Param Data field contains either a 0
or a 1 informing the U60 that the following
message is either a non-priority message
(0) or a priority message (1). The U60
driver does not use priority messaging;
therefore, this value is ignored. This
allows the U60 to respond to the
CpMsgReq based on actual buffer
availability.
Alternatively, you can send the entire
CpMsg plus message to the U60 and a
CpMsgReject may be sent uplink if there
are no available buffers.
D
4 CpMsgAck The U60 is entering the ready-receive
state. This is the U60’s response to the
CpMsgReq .
U