Switch to Command Mode Request
The host computer may issue command
#01 Switch to Command Mode
while in data mode.
The basic protocol format is as follows:
<som><cmd><eom>
The ECP format is as follows:
<som><seq><cmd><crc><eom>
where
<som>
Start-of-message (ASCII # character)
<seq>
Sequence number generated by the host computer separately from that appearing in
data messages transmitted by the Encompass 4 Reader
<cmd>
Switch to command mode (ASCII characters 01)
<crc>
CRC value for the message
<eom>
End-of-message character (ASCII CR)
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 Encompass 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
Chapter 6 Communications Protocols
TransCore Proprietary
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