TransCore SmartPass AI1611, System Manual

Page: 118 / 179

Communication Protocols
Illegal Command
If the reader receives an illegal command, it will return its standard Error message.
Transmission Timeout
If the reader transmits an asynchronous message and the host does not send an
ACK
before the ECP timeout occurs, the reader will retransmit the message.
Receive Timeout
If the reader receives a
<som>
but does not receive a matching
<eom>
before the
ECP timeout occurs, it will discard the incomplete message and reset its receiver.
Asynchronous Message/Command Message Collision
If the reader transmits asynchronous data at the same time the host sends a
command, the reader will give priority to receiving the command. It will process the
command and send a message before it retransmits the asynchronous data.
Host Addressed Failure Conditions
The host addresses the following failure conditions.
Illegal or Wrong Sequence Number
If the host detects an illegal or wrong sequence number in a reader response, it
should retransmit the command with the same sequence number. If the host detects
an illegal sequence number in an asynchronous reader transmission, it should send a
NAK
message.
Bad CRC
If the host detects a bad CRC in a reader message, it should retransmit the command
with the same sequence number. If the host detects a bad CRC in an asynchronous
reader transmission, it should transmit a
NAK message.
Transmission Timeout
If the reader does not respond to a host command within a specified interval, the host
should retransmit the command with the same sequence number.
Receive Timeout
If the host receives a
<som>
but does not receive a matching
<eom>
within a
specified timeout interval, it should discard the incomplete message and reset its
receiver.
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