IRCC2.0 SMSC Corporation, IRCC2.0 Datasheet - Page 21

• Manufacturer Part Number: IRCC2.0
• Description: Infrared Communications Controller
• Manufacturer: SMSC Corporation

BOF Counting
The IrCC 2.0 can account for system-dependent
limitations such as long interrupt latencies and
transceiver stabilization times by increasing the
number of STA flags at the beginning of every
HDLC frame (Figure 14).
Back-to-Back Frame Transmission
Back-to-back, or brick walled frames are allowed
with two or more flags, '7E'hex, in between. If
two consecutive frames are not back-to-back, the
gap between the last STO flag of the first frame
and the first STA field of the second frame are
separated by at least seven bit times (abort
sequence).
CCITT 16-bit
CRC
FCS
Previous
Frame
'01111110'
binary
STA
'01111110'
binary
STO
FIGURE 14 - EXTENDED BEGINNING-OF-FRAME
FIGURE 15 - BRICK WALLED HDLC FRAMES
Appends 0 - 4095 Flags to
'01111110'
BOF COUNT register
Beginning of Frame
binary
STA
'01111110'
binary
STA
Inserts 0 - 4095 Flags between
8-bit Address
ADDR
'01111110'
Field
Brick Walled Frames
BW COUNT register
binary
STA
21
8-bit Address
8-bit Control field plus up to 2K - 3 bytes
ADDR
Field
The BOF COUNT register contains the number
additional start flags that are to be appended to
the standard BOF characters. Note: The BOF
COUNT extensions only apply to messages that
start from an idle line state; i.e., BOF counting
does not apply to brick walled messages.
The IrDA FIR 1.152 Mbps and 0.576 Mbps
physical layer specification allows back-to-back
message packets with three flag characters,
which act as the closing flag of the first frame
and the opening flags of the brick, walled packet.
Additional flags can be added by programming
the Brick Wall Count register (Figure 15). Note:
The BOF COUNT extensions do not apply to
brick walled messages.
Information Field
Brick Walled Frame
8-bit Control field plus up to 2K - 3 bytes
DATA
Information Field
DATA