Intermec Sabre 1555, Programmer'S Reference Manual

Page: 46 / 178

Sabre 1555 RFID & Bar Code Reader Programmer’s Reference Manual
4-6
Maximum Frame Size
A message consists of one or more frames. For messages with more than one frame,
each frame has a maximum size of 255 bytes (STX to ETX).
The maximum size of the message depends on the capacity of the receiver’s input
buffer.
However, if an application has limited resources, the maximum frame size can be
decreased by setup configuration.
Proprietary DLE (Data Link Escape)
To avoid frame desynchronization, proprietary DLE encoding is applied if the
following values are encountered inside the formatted frame (not including the STX/
ETX delimiters):
STX/ETX (0x7F), DLE (0xEE)
1. The proprietary DLE character (0xEE) is inserted before the ambiguous
character.
2. The value of the ambiguous character is increased by 1.
Note: This method simplifies processing of delimiter localization as the ambiguous
character can not be mistaken for a delimiter.
<FRAME_MANAGEMENT > 1 byte Bits 7, 6 (<More>), indicates that the message is not
finished (another frame being sent)
Bits 5, 4, and 3 are not used
Bit 2 (<AccRequest>), request high-level
acknowledgment for the command
Bit 1 (<RestartFlag>), product/host restart indicator
Bit 0 (<FrameNumber>), frame sequence indicator
< CHK > 2 bytes The first byte is the most significant byte (MSB) and
the second byte is the least significant byte (LSB).
Sum with weight calculation (in “Checksum
Calculation” on page 4-13)
< ETX > 1 byte Delimiter, value of 0x7F
Table 4-3 Frame Format Components (continued)
Item Length Description