ST75C540 datasheet(69/84 Pages) STMICROELECTRONICS

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XI - TRANSMITTING DATA IN PARALLEL MODE (continued)

XI.6.7 - HDLC Special Timming

DATA TRANSMITTED

7E..7E 7E

DATA

CRC

_NHFBF

7E..7E 7E

CRC

_NHFCF

7E 7E..7E

_NHFST

Time to fill the Buffer 0

(Otherwise Extra

Flags Added)

Time

to fill the

Buffer 1

Time

to fill the

Buffer 0

DATA

Time to fill the

Buffer 1(Otherwise

Extra Flags Added)

Time

to fill the

Buffer 0

FORM 2

XMIT 1

XMIT 0

STOP

Figure 36

A set of global variables allows the programmation

of the number of flags (7E) generated by the

ST75C530/540 :

- _NHFBF : Number of flags before the first frame.

- _NHFCF : Number of flags between frames.

- _NHFST : Number of flags after the last frame.

The default value for all these variables is 0, the

programming range is from 0 to 7FFF (32767).

These varaibales must be modified with a MW or

MWI command (see Figure 36).

XI.7 - UART Mode Description

In UART mode the ST75C530/540 transmits the

data Character contained into the DUAL Ram

buffe. The mechanism is as follows :

- While the Host has no character to transmit, that

i s: as long as DTTBSx equals $ 00, the

ST75C530/540 transmits continuous “1”.

- When the Host wants to send a chacarter,it feeds

the buffer with the character to transmit.

- The ST75C530/540 start to send a stop bit (“0”)

then the character containedin the Buffer,comput-

ing the parity. It send the parity bit, if needed, and

the stop bits (1 or 2 according with the FORM

command).

- If the user wants to send a break signal, he has

to set the BUFF_UBRK bit within the correspond-

ing Status Word (DTTBSx). A break signal is

defined as a totaly null character with all stop bits

duration maintained to “0” (e.g: if format is 7 bit,

even parity and 2 stop bit, break is a ”0” durring

10 bit). Multiple continuous breaks (“0” continu-

ous signal) can be send by using consecutive

buffers with BUFF_UBRK set to 1.

XI.7.1 - Status Word Format

DTTBSx in UART Mode

Field

Pos. Value

Definition

BUFF_LENG 3 .. 0

other

Buffer empty.

1 character to transmit

(

DTTBFx[0]).

Not allowed.

BUFF_UBRK

Normal character.

Break signal : a complete

“0” character with all stop

bits equal to ”0”.

Other

Reserved, must be 0.

ST75C530 - ST75C540

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