
SapIP – IRT Instruction Manual 1/23/2017
Page 42
Dynamax, Inc.
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Test Condition: If the coordinator is powered down right before a transmission. In that case the end
radio thinks it’s associated but the connection is broken. The LED will blink fast while attempting
to transmit. That is the associated blink code, but it can’t complete the transaction for whatever
reason (out of range or something). After 10 seconds with no ack’s coming back, the end radio is
hardware reset. So then when the coordinator and network have healed then the unit will start a
normal timing cycle. That reset will prevent the end device from permanently locking out of the
network.
4.
Communication Failures
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If there is noise on the channels data may be corrupted between end device and coordinator. This
may show up in various ways:
4.1
Data is corrupted when received at coordinator
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Coordinator sends a nack, in which case the CPU substitutes an ‘N’ for the record number
and retransmits it. That re-transmission also requires an ack/nack. If four nacks in a row are
received, the packet is discarded and the next measurement cycle is started. So if a record
shows up at the coordinator with a record number of ‘N’ then that means that a defective
packet was nack’ed and successfully retransmitted.
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Be aware that the MAC layer of the Zigbee protocol also does ack/nacks and retransmissions.
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See the Zigbee documents for details. Ref TBD.
4.2
Incoming Packet is Corrupted before Parsing
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An ack/nack packet has a checksum — if it fails the checksum test then the original outgoing
data packet is retransmitted. But the record number now is a ‘C’. That could possibly result in
additional packets arriving at the coordinator application layer.
5.
Incoming Packet Has the Incorrect Size
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The size of the ack/nack packet received is compared to the size indicated in bytes 1 & 2 of
that packet. If they don’t match a ‘P’ becomes the record number data transmission, and the
original packet is retransmitted.
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Occasionally a status packet comes in, for example when the network rejoins a status packet
arrives with that information. That packet is ignored as well as all others that are not
recognized. No action is taken.