ST75C520 datasheet(40/45 Pages) STMICROELECTRONICS

40 / 45 page

IX.4 - Buffer Status and Format Description

The following section describes the meaning and

use of the buffer status words.

IX.4.1 - Transmit Buffer

The transmit buffer status words are DTTBS0 and

DTTBS1 (see the Host Interface Summary sec-

tion in the main document) and are more likely to

be seen as control words. These words must be set

by the host and are reset by the ST75C520. The

data buffer exchanges are synchronized through

these status words, (see Buffer Status and format

description) an improper setting will trigger the error

Err_Tx in the error status SYSERR. A value of 0 for

DTTBS0 or DTTBS1 means that the corresponding

buffers are empty : this value is written by the

ST75C520. The unused bits of DTTBSx must be

set to 0 by the host.

In FSK Mode, when working in the parallel data

mode, the transmitter expands each bit to the

nominal baud time (1200Hz/300Hz/75Hz).

IX.4.2 - Synchronous Mode

Field

Pos.

Val.

Description

BUFF_LENG

3..0

1..8

Number of valid

bytes in the buffer

IX.4.3 - HDLC Framing Mode

Field

Pos.

Val.

Description

BUFF_LENG

3..0

1..8

Number of valid

bytes in the buffer

BUFF_SFRM

Data stream

Start of frame

BUFF_EFRM

Data stream

End of frame

BUFF_FRAB

Normal process

Abort frame (no

data in buffer)

IX.5 Receive Buffer

The receive buffer status words are DTRBS0 and

DTRBS1 (see the Host Interface Summary sec-

tion in the main document). These flags are set by

the ST75C520 and must be reset by the host. The

data buffer exchanges are synchronized through

these status words, an improper resetting will trig-

ger the error Err_Rx in the error status SYSERR. A

value of 0 for DTRBS0 or DTRBS1 means that the

corresponding buffers are empty : this value must

be written by the host.

In FSK or V.21 Channel 2 Mode, when working in

the parallel data mode, the receiver extract each

bi t

u s ing

t h e

nomi n al

baud

r at e

(1200Hz/300Hz/75Hz).

IX.5.1 - Synchronous Mode

Field

Pos.

Val.

Description

BUFF_LENG

3..0

1..8

Number of valid

bytes in the buffer

IX.5.2 - HDLC Framing Mode

Field

Pos.

Val.

Description

BUFF_LENG

3..0

1..8

Number of valid

bytes in the buffer

BUFF_ERRS

5..4

No error

CRC error

Non byte-aligned

frame

Aborted frame

BUFF_SFRM

Data stream

Start of frame

BUFF_EFRM

Data stream

End of frame

IX.6 - Data Buffer Management

Figure 9 shows the general flow chart for transmit

data buffer management. In the transmit path, the

data buffer exchanges should always begin with

the filling of buffer 0, then with the update of the

buffer 0 status word. The initiation of the data

exchanges is initiated then with the XMIT com-

mand.

ST75C520

40/45

ST75C520 数据表(PDF) 40 Page - STMicroelectronics

ST75C520 数据表(HTML) 40 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

数据表下载

链接网址

ST75C520 数据表(PDF) 40 Page - STMicroelectronics

ST75C520 数据表(HTML) 40 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

数据表 下载

链接网址

数据表下载