User manual

REFERENCES
151
Frame Packing
When Frame Packing is disabled, the Output Message
from the Gryphon™ BT
reader is sent to the Host as is, see par. 5.3.
If instead, Frame Packin
g is enabled, the Output Message is "packed" into a Frame
with the following format:
STX Length Control Counter Output Message CRC-16 CR
where:
STX = Frame Start character (02 Hex).
Length = 2 bytes; indicates frame length of the remaining fields (including CR).
Control = 1 byte; indicates message fragmentation. For further details see the DL
Security Protocol documentation on the CD-ROM.
Counter = a loop counter for the Output Message characters (bytes) that cycles from
0 to 255 and then restarts.
Output Message = complete text message from the Gryphon™ BT reader including
optional fields as shown in par. 5.3. The maximum length of this field is 304 bytes.
CRC-1
6) =
2 bytes; 16-bit Cyclic Redundancy Check based on the hex 1021
polynomial and performed on all bytes from Length up to the CRC itself. The MSB is
sent first. For further details see the DL Security Protocol documentation on the CD-
ROM.
CR = Frame Stop character (0D Hex).
To simplify the management of this frame packing, and to avoid having to develop a
special proprietary software program, included on the CD-ROM are: the DL Security
Protocol example program, (written in Visual Basic), the Windlbt.dll, and the source
code of the example. The example program allows extraction of the data from the
frame, verification of the CRC, discarding any duplicate data (with the same counter
value), and automatic management of Frame Packing and ACK/NACK protocol in
response to each frame.
5.8.2 User Friendly Name
This parameter provides a way to identify the Gryphon™ BT reader in a human
readable (user-friendly), format. This name is returned with the reader configuration
parameters (see par. 6.2). The name is made up of a fixed 20-character field. If you
choose to use
a name that is less than 20 characters, you must fill in the blanks with
a valid character (i.e. space character). Valid characters are in the range 00 - 7E and
must be entered in hex format.