Echelon LonTal Stack - Manual (Page 54)

42 Creating a LonTalk Stack Serial MIP Driver
Type Code Values
The following table lists the values for the Type Code byte. Uplink means that
data is transferred from the Echelon Smart Transceiver or Neuron Chip to the
host processor. Downlink mans that data is transferred from the host processor
to the Echelon Smart Transceiver or Neuron Chip.
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 Serial MIP and
requesting an uplink CpMsgAck.
The Param Data field contains either a 0
or a 1 informing the Serial MIP that the
following message is either a non-priority
message (0) or a priority message (1).
The MIP Serial driver does not use
priority messaging; therefore, this value
is ignored. This allows the Serial MIP to
respond to the CpMsgReq based on
actual buffer availability.
Alternatively, you can send the entire
CpMsg plus message to the MIP and a
CpMsgReject may be sent uplink if
there are no available buffers.
D