IRCC datasheet(21/79 Pages) SMSC

21 / 79 page

HDLC BOF Counting

The IrCC 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.

HDLC Back-to-Back Frame Transmission

HDLC 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 1.152Mbps and .576Mbps 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

IRCC データシート(PDF) 21 Page - SMSC Corporation

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