TransCore SmartPass AI1611, System Manual

Page: 110 / 179

Communication Protocols
character. The reader will issue an
Error
message and the host a negative
acknowledgment message.
Data Inquiry Protocol
Data inquiry protocol is a basic protocol option that allows the host to control
transmission of reader tag data. The selection of data inquiry protocol affects data
mode operation. As the reader acquires tags, it buffers them but does not transmit
them. Instead, the host must poll the reader for each tag by sending a CTRL-E
character (hex 5 digit). The reader transmits one message (tag or report data) for
each CTRL-E it receives until the buffer is empty.
Each tag request message sent by the host consists only of the CTRL-E character; no
som or eom characters are sent. The reader data transmission (tag and report data)
format is the same as for basic protocol.
Selection of data inquiry mode does not affect command mode operation.
Basic and ECP Protocol Formats
Note: In the following text, the symbols
<
and
>
are used to represent required
variable message data, and the symbols
[
and
]
are used to represent
optional data. These symbols are not part of the message syntax.
Reader Transmissions
The basic protocol format and the data inquiry protocol format are:
<som><data><eom>
The ECP format is:
<som><seq><data><crc><eom>
where
<som>
Start-of-message (ASCII # character
)
<seq>
Sequence number (ASCII hex) that represents an even
number in the range 0–9, A–E. This number is maintained
by the reader. The host must acknowledge reader
transmissions by sending an
ACK
message with the same
sequence number received from the reader. The reader will
update its sequence number upon receipt of a valid host
ACK
. If an
ACK
is not received, the reader will retransmit the
message. A reader transmission sequence is not considered
complete until the reader receives a valid
ACK
and updates
its sequence number.
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