TPU2735 Просмотр технического описания (PDF) - Unspecified

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производитель

TPU2735

Teletext Processor

Unspecified 

TPU 2735

4. Various Operation Modes of the TPU 2735

4.1. The Menu Mode

In the menu mode, on the screen of the TV set is dis-

played a list of contents of the RAM. This list is achieved

by displaying row 0 of all sectors at the same time (Fig.

4–1). Each row 0 is supplemented by the sector number

and the requested page number. These two informa-

tions are placed at the beginning of each row 0 in the

same way as the status indicator. The menu is displayed

immediately if MEN (R-DC1) is set to 1. The lower part

of the menu cannot be displayed in double-height mode.

status indicator

0

> 3 1 5 (page header of selected sector)

1

2

3

4

5

1 311

row 0 of sector 0

6

7

2 312

row 0 of sector 1

8

9

3 314

row 0 of sector 2

10

11

4 315

row 0 of sector 3

12

13

5 410

row 0 of sector 4

14

15

6 120

row 0 of sector 5

16

17

7 210

row 0 of sector 6

18

19

8 150

row 0 of sector 7

20

21

22

23

Fig. 4–1: Display of the menu on the screen

(example)

4.2. Teletext Display without Interlaced Lines

In this operation mode, the flicker of the TV screen is re-

duced. For this, the TPU 2735 can distinguish between

field 1 and field 2 of a TV frame. If the TPU 2735 is sup-

plied by sync signals without interlace, the character

rounding of normal height characters is switched off

automatically thus enabling a balanced display of a

Teletext page displayed without interlaced lines. The

DPU 25.. Deflection Processor Unit can provide appro-

priate sync signals on request of the CCU.

When a subtitle or a newsflash page is displayed with

both TV picture and Teletext characters on the screen,

the TPU 2735 sets a flag (TVS = 1 in R-DC3) to indicate

that a display with interlaced lines is referable.

4.3. The Effect of Errors in the Transmission of

Teletext Data

4.3.1. Errors in the Hamming-Code Protected Data

Single errors are corrected and have no further effect.

Rows with multiple errors are not loaded into the DRAM.

The error flag of this page number is set and the TPU

tries to read this page when it occurs again without clear-

ing the previously acquired data.

4.3.2. Errors in Data with Parity Check

Data with parity errors is not written to the RAM. A parity

error sets the error flag of the received page number.

The TPU tries to read this page again without clearing

the previously acquired data.

4.4. Multipage Conflict Situation

A conflict situation arises if the TPU 2735 receives a new

page while the reception of another requested page has

not been finished. This situation comes up if requested

pages of different magazine numbers are transmitted

with interleaved rows or if the last page of a block of

pages from the same magazine is requested.

In a conflict situation only the first page is stored immedi-

ately. The others have to wait until they are transmitted

again. A page which has a conflict with another page

loses its priority over the following page when it is stored

and regains priority when all pages involved in a conflict

have been stored. The selected page does not loose its

priority to guarantee the updating of the display.

15

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