TransCore 05531 User Manual
Encompass 4/4800 Multiprotocol Reader System Guide
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After the Encompass 4/4800 Multiprotocol Reader receives new communications
parameters, the Encompass 4/4800 Multiprotocol Reader issues the Done message
and switches to the new configuration immediately. The host computer switches its
communications parameters immediately after the transaction is complete.
parameters, the Encompass 4/4800 Multiprotocol Reader issues the Done message
and switches to the new configuration immediately. The host computer switches its
communications parameters immediately after the transaction is complete.
As noted, the message
initiator, such as the Encompass 4/4800 Multiprotocol Reader
in data mode and the host computer in command mode, starts a timeout counter at the
time a message is transmitted. If the timeout expires before receiving an acknowledge-
ment message, a logical NAK condition is declared, and the initiator assumes the mes-
sage was received in error. In this instance, the message is retransmitted until an
acknowledgement message is received.
time a message is transmitted. If the timeout expires before receiving an acknowledge-
ment message, a logical NAK condition is declared, and the initiator assumes the mes-
sage was received in error. In this instance, the message is retransmitted until an
acknowledgement message is received.
The message recipient, such as the host computer in data mode and the Encompass 4/
4800 Multiprotocol Reader in command mode, starts a timeout counter when a
<som>
4800 Multiprotocol Reader in command mode, starts a timeout counter when a
<som>
character is received. If the timeout expires without the receipt of an <eom>,
the message acquisition is aborted (reset), and the receiver waits for the next <som>
character.
character.
If the message recipient receives a second <som> character before an <eom> charac-
ter, the message acquisition is aborted (reset), and retransmission of the previous mes-
sage is assumed to be underway.
ter, the message acquisition is aborted (reset), and retransmission of the previous mes-
sage is assumed to be underway.
These strategies allow for recovery during periods when communications are marginal
or completely lost.
or completely lost.
Note: It is important that the host computer limit the period during which the Encom-
pass 4/4800 Multiprotocol Reader remains in command mode to avoid losing tag IDs.
RF is off in command mode and no tags can be read.
pass 4/4800 Multiprotocol Reader remains in command mode to avoid losing tag IDs.
RF is off in command mode and no tags can be read.
Reader-Addressed Failure Conditions
The Encompass 4/4800 Multiprotocol Reader addresses the following failure condi-
tions.
tions.
Illegal Sequence Number (not in the range 0–9, A–F)
If the Encompass 4/4800 Multiprotocol Reader 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
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 Encompass 4/4800 Multiprotocol Reader receives the wrong sequence number
in an ACK
in an ACK
message, it responds as if a
NAK
had been received, and it retransmits the
data.
Incorrect CRC
If the Encompass 4/4800 Multiprotocol Reader 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.
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.