TransCore encompass 4, Manual

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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 Encompass 4 Reader
acquires tags, it buffers them but does not transmit them. Instead, the host must poll the Encompass 4
Reader for each tag by sending an ASCII CRTL-E character (hexadecimal 05). The Encompass 4 Reader
transmits one message (tag ID 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. Encompass 4 Reader data transmission (tag ID and report data) format is the same as
for basic protocol.
Selection of data inquiry protocol does not affect command mode operation.
Basic Protocol and ECP Format
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 as follows:
<som><data><eom>
The ECP format is as follows:
<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–F (0, 2, 4, 6, 8, A, C, E). The Encompass 4 Reader maintains the number. The host
must acknowledge reader transmissions by sending an ACK message with the same
sequence number received from the Encompass 4 Reader. The Encompass 4 Reader
updates its sequence number upon receipt of a valid host ACK . If an ACK is not
received, the Encompass 4 Reader retransmits the message. A reader transmission
sequence is not considered complete until the Encompass 4 Reader receives an ACK
and updates its sequence number.
<data> An ASCII string up to 72 characters long. This string may contain tag data, a presence
without tag report; an input status change report; an Error06, Error07,
Error08, or Error11 message; or a sign-on message. Auxiliary data may also be
included.
<crc>
Field containing four ASCII digits that represent the 16-bit CRC value calculated on the
message. The CRC value is calculated on bytes between the
som
character and the first
<crc>
byte.
Chapter 6 Communications Protocols
TransCore Proprietary
6–73