ST75C530 datasheet(63/84 Pages) STMICROELECTRONICS

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X.6 - FORM Command

The FORM command allows the selection of the

Data Format. The Parameter syntax is as follows :

Field

Byte Pos. Value

Definition

X_SYNC

2..0

000*

001

010

011

100

Synchronous format

T ransmit continuous

“1”

(1)

HDLC framming

T ransmit continuous

”0”

(1)

UART

X_ANBIT

1..0

7 Bit per character

8 Bit per character

X_APAR

3..2

No parity

Even parity

Odd parity

X_ASTOP

1 stop bit(1)

2 stop bit(1)

Note : 1. Transmit only

X.6.1 - Synchronous Mode

The synchronous mode is the default mode, if no

FORM command is used.

The transmitter reads the bits in the DUAL Ram

Buffer DTTBFx (starting with the Bit 0 of Byte 0 of

Buffer 0) and send them over the Telephone line.

The Buffer Status Byte

DTTBSx contains the num-

ber of Data Bytes to transmit.

The Receiver write the received bits coming from the

Telephone line and write them into the DUAL Ram

Buffer

DTRBFx (startingwith the Bit 0 of the Byte 0 of

theBuffer0).TheBufferStatusByteDTRBSx contains

the number of Data Bytes received (generaly 8).

The time betweeneach IT2 interrupts(or IT3) is equal

to 64-bit if the number of Data Bytes is set to 8. The

Host has the full 64 bits time to serve the interrupt :

Bit Rate (bps)

Interrupt Time (ms)

14400

12000

9600

7200

4800

2400

1200

300

4.4

5.3

6.6

8.8

13.3

26.6

53.3

213.3

853.3

X.6.2 - HDLC Mode

The HDLC Format can be used for T.30 or ECM

implementations

X.6.2.1 - HDLC Transmit

TheHDLC Transmitter performsthe following tasks :

- Flag generation (7E) while in inter-frame.

- Flag generation (7E) at the begining of a frame.

- Zero insertion (after 5 consecutive “1”).

- CRC16 computation.

- CRC16 transmission at the end of a frame.

- Flag generation (7E) at the end of a frame.

- Abort frame.

- Programmable number of Starting flags.

- Programmable number of Inter frame flags.

- Programmable number of Ending flags.

The Buffer Status Byte

DTTBSx defines the frame

type, and the number of Data Bytes to transmit.

X.6.2.2 - HDLC Receive

The HDLC Receiver performs the following tasks :

- Flag recognition.

- Opening flag recognition.

- Zero deletion.

- CRC16 computation.

- CRC16 check ; error CRC16 detection.

- Closing flag recognition.

- Abort frame detection.

- Received CRC.

The BufferStatusByte DTRBSx containsthe frame

type, the number of Data Bytes and the error report

if any. The errors detected are :

- CRC16 Error : Wrong CRC received.

- Non byte-alligned frame : The number of Data bits

betweenthe beginingoftheframe andtheendof the

frame (after “zero” deletion) is not a byte- multiple.

- Aborted frame : More that 6 consecutive “1” re-

ceived.

X.6.3 - UART Mode

In the UART mode the buffers contains only one

Character to transmit or received. The worse case

of interruptrate is obtained with the lower character

bit length (7bit of data, no parity and 1 stop bit) and

is provided in the following table.

Bit Rate (bps)

Interrupt Time (ms)

14400

12000

9600

7200

4800

2400

1200

300

0.41

0.82

1.25

1.64

3.75

7.5

120

X.6.3.1 - UART Transmit

The UART Transmitter performsthe following tasks :

- Start bit generation.

- Parity Computation.

- Stop Bit generation.

- Break generation.

X.6.3.2 - UART Receive

The UART Receiver performs the following tasks :

- Start bit recognition.

- Parity Checking.

- Stop bit Checking.

- Break detection.

X - PARALLEL DATA EXCHANGE (continued)

ST75C530 - ST75C540

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