TransCore AI1422E, User Manual

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The request command format is as follows:
<7EH><7EH><42H><CRC>
The response is
<7EH><7EH><01H><transponder count><transponder ID><CRC>
Table 5 Retransmit Request Message Fields
Field Description Hex ASCII
Start of Message
These two bytes, along with the Message Type
byte, designate the start of the data message.
7E7E ~~
Message Type
Sending a 42H indicates that this message is a
retransmit request.A
42 B
Cyclical
Redundancy Check
An 8-bit cyclical redundancy check (CRC)
Includes the Start of Message and Message
Type. Refer to Appendix E on page E–84 for a
description of the CRC algorithm. This is a fixed
value of 42 hexadecimal, for this command.
There is no carriage return or line feed for this
message.
42 B
Table 6 Retransmit Response Message Fields
Field Description Hex ASCII
Start of Message
These two bytes, along with the Message Type
byte, designate the start of the data message.
7E7E ~~
Message Type
An 01H indicates that this message is a tag data
message.
01 SOH
Transponder Seen
Count
After power-up, this 8-bit count begins with 01
and is updated each time a tag with a unique ID
moves out of the RF field, then back into the RF
field. This field is useful in determining whether
a train has multiple tag reads of a given ID due
to a change in the train’s direction.
00 - FF N/A
Transponder ID
The data that is programmed into the
transponder. The data within the transponder
is 6-bit ASCII but the interrogator translates this
data into standard 8-bit ASCII.
Hex ID ID
Cyclical Redundancy
Check
An 8-bit cyclical redundancy check (CRC).
Includes the Start of Message, Message Type,
Seen Count and Transponder ID. Refer to
Appendix E on page E–84 for a description of
the CRC algorithm. There is no carriage return
or line feed for this message.
00 - FF N/A
Chapter 6 Commands
TransCore Proprietary 6–25