IRCC datasheet(22/79 Pages) SMSC

22 / 79 page

4PPM BOF Counting

The IrCC can account for system-dependent

limitations such as long interrupt latencies and

transceiver stabilization times by increasing the

number of PA flags at the beginning of every

4PPM frame (Figure 16).

The BOF COUNT register contains the number

of additional PA bytes that are to be appended to

the standard 4PPM 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.

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

ADDR

8-bit Address

Field

DATA

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

Information Field

BOF COUNT register

Appends 0 - 4095 PA Bytes

to Beginning of Frame

...

PA (#16)

PA (#1)

STA

8-bit Start

Field

FIGURE 16 - 4PPM EXTENDED BOF

IRCC 数据表(PDF) 22 Page - SMSC Corporation

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