TransCore MPRX, System Manual

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MPRX
TransCore Proprietary 6–11
Reader-Addressed Failure Conditions
The MPRX addresses the following failure conditions.
Illegal Sequence Number (not in the range 0–9, A–F)
If the MPRX detects an illegal sequence number in a host command message, it discards
the received message and sends no response. If it receives an illegal sequence number in
an
ACK
message, it responds as if a
NAK
had been received and retransmits the data.
Wrong Sequence Number
If the MPRX receives the wrong sequence number in an
ACK
message, it responds as if a
NAK
had been received, and it retransmits the data.
Incorrect CRC
If the MPRX detects an incorrect CRC value in a host command message, it discards the
received message. No response is sent. If it receives an incorrect CRC value in an
ACK
message, it responds as if a
NAK
had been received, and it retransmits the data.
Illegal Command
If the MPRX receives an illegal command, it returns its standard
Error
message.
Transmission Timeout
If the MPRX transmits an asynchronous message and the host does not send an
ACK
before the ECP timeout occurs, the MPRX retransmits the message.
Receive Timeout
If the MPRX receives a <som> but does not receive a matching <eom> before the ECP
timeout occurs, it discards the incomplete message and resets its receiver.
Asynchronous Message/Command Message Collision
If the MPRX transmits asynchronous data at the same time that the host sends a command,
the MPRX gives priority to receiving the command. It processes the command and sends
a message before it retransmits the asynchronous data.
Host-Addressed Failure Conditions
The host device 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 retransmits
the command with the same sequence number. If the host detects an illegal sequence
number in an asynchronous reader transmission, it sends a
NAK
message.
Incorrect CRC
If the host detects an incorrect CRC value in a reader message, it retransmits the command