MagTek PORT POWERED - Manual (Page 21)

Section 3. Commands, Formats, Timing
15
Where
SS = Start Sentinel: "%" for Track 1; ";" for Track 2; "+" for Track 3
Data = Track Data in track order
that is, Track 1 then Track 2 or Track 2 then Track 3
ES = End Sentinel: "?"
Sensor = "0" no card in reader
"1" card present in reader (rear sensor blocked)
If there is an error in one of the tracks, the "Track Data" field will be replaced with "E" (0x45).
An example of a card insertion or removal is as follows:
Where
1 = Sensor blocked
0 = Sensor unblocked
The following is an example of a good read on withdrawal of a card:
Where 0 represents the sensor unblocked.
The following is an example of a bad read on Track 1 and a good read on Track 2 on withdrawal
of a card:
Where
E (0x45) = Error
Track 2 Data = Good read Track 2 Data
0 = Sensor unblocked
STX ESC % E ? ; Track 2 Data ? 0 CR ETX
Optional
STX ESC % Track 1 Data ? ; Track 2 Data ? 0 CR ETX
Optional
STX ESC 1 CR ETX
Optional