IRCC2.0 datasheet(21/87 Pages) SMSC

21 / 87 page

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).

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.

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).

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.

ADDR

8-bit Address

Field

STA

'01111110'

binary

DATA

8-bit Control field plus up to 2K - 3 bytes

Information Field

STA

'01111110'

binary

BOF COUNT register

Appends 0 - 4095 Flags to

Beginning of Frame

FIGURE 14 - EXTENDED BEGINNING-OF-FRAME

ADDR

8-bit Address

Field

STO

'01111110'

binary

FCS

CCITT 16-bit

CRC

DATA

8-bit Control field plus up to 2K - 3 bytes

Information Field

Brick Walled Frame

Frame

STA

'01111110'

binary

BW COUNT register

Inserts 0 - 4095 Flags between

Brick Walled Frames

STA

'01111110'

binary

FIGURE 15 - BRICK WALLED HDLC FRAMES

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