Communications Protocols
6-5
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 a CTRL-E character (hex 5 digit). 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 vari-
able 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
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