TransCore encompass 4 - Host Transmission

Encompass 4 Reader System Guide
6-8
Host Transmission
The host computer initiates synchronous communications between the Encompass 4
Reader and the host. The host begins a sequence by issuing a command; the Encom
-
pass 4 Reader responds accordingly.
The data inquiry protocol format is as follows:
<CTRL-E>
The basic protocol format is as follows:
<som><cmd>[<data>]<eom>
The ECP format is as follows:
<som><seq><cmd>[<data>]<crc><eom>
where
<CTRL-E> ASCII Control E (hex 5 digit). When in data inquiry mode, each
transmission of a CTRL-E by the host causes the Encompass 4
Reader to transmit one tag ID.
<som> Start-of-message (ASCII # character)
<seq> Sequence number (ASCII hex digit) that represents an odd
number in the range 0–9, A–F (1, 3, 5, 7, 9, B, D, F). The host
should use odd sequence numbers in its command since the
Encompass 4 Reader uses even sequence numbers in its
transmissions. This method eliminates the possibility of a
synchronous host command and an asynchronous reader
transmission having the same sequence number.
Upon receiving a host command in ECP, the Encompass 4 Reader
replies using the command’s sequence number in its response.
Therefore, the host computer updates its sequence number upon
receipt of a valid reader message. If the sequence number is not
updated before transmission of the next command, the
Encompass 4 Reader will not service the new command; it will
retransmit its previous message. A command/message sequence
is not complete until the host updates its sequence number.
<cmd> Command code, a string that contains from two to four ASCII
hex characters
[<data>] Optional data field, an ASCII string of as many as 20 characters
in length. For example, the store hardware configuration string
command is #696S...S or command #696 Store Hardware
Configuration String followed by the data string S...S.
<crc> CRC value for the message