ST75C540 datasheet(64/84 Pages) STMICROELECTRONICS

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FORM 3

XMIT 1

XMIT 0

XMIT 1

FORM 2

XMIT 0

STA_106

DATA

TRANSMITTED

COMMANDS :

$7E

Figure 26

XI - TRANSMITTING DATA IN PARALLEL MODE

XI.1 - Description

XI.1.1 - XMIT Command

The XMIT Command works like a CTS signal for

the Parallel Data process.

When XMIT is off, the ST75C530/540 transmits

continuous “1”. When on the ST75C530/540trans-

mits Data in accordance with the FORM command

and starts to manage the Data Buffer.

This command can be sent at any time, while in

Data Mode (see Table below).

XI.1.2 - FORM Command

The FORM Command can be sent at any time to

redefine the current format. The effect will take

place only when XMIT is on.

Here is a formal example showing the relationship

between XMIT, and FORM Commands (see Fig-

ure 26).

XI.1.3 - STOP Command

The

STOP command is used, at the end of the

transmission, to stop sending the carrier on the

telephone line.

Prior to the STOP command the user must have

stop the parallel transmition with a

XMIT off com-

mand.

When the current data buffer will be totaly transmit-

ted, and that no more buffers will be available, that

is to said both

DTTBF0 and DTTBF1 will be $00

(equivalent to an Underrun condition).

XI.1.4 - Timing

Here are regular sequences to stop properly the

transmition (see Figure 27).

Field

Byte Pos. Value

Definition

TX_START

0 *

(Off) Send

continuous “1”

(**).

( O n) Send Dat a

according with the

Format defined in the

FORM command.

The

XMITOff command takes effect only when the two Transmit

buffers are empty : DTTBF0 and DTTBF1 equal to $00.

Feed Last Buffer

XMIT 0

STOP

Feed Last Buffer

XMIT 0

STOP

DATA

TRANSMITTED

STA_106

DATA

TRANSMITTED

STA_106

(ignored until here)

$7E

CRC16

Last Buffer

Case # 1 Synchronous Format

Case # 2 HDLC Format

Case # 3 UART Format

XMIT 0

STOP

DATA

TRANSMITTED

STA_106

(ignored until here)

Last Buffer

Figure 27

ST75C530 - ST75C540

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