TDA9554PS datasheet(41/125 Pages) PHILIPS

41 / 125 page

2000 Jun 22

Philips Semiconductors

Tentative Device Speciﬁcation

TV signal processor-Teletext decoder with

embedded

µ-Controller

TDA955X/6X/8X PS/N1 series

when a page header is received for that page. The bit in

the SPT is set when a page header for the page is received

which has the ‘subtitle’ page header control bit (C6)

set.The bit for a particular page in the TPT is set when a

page header is received for that page. The bit in the SPT

is set when a page header for the page is received which

has the ‘subtitle’ page header control bit (C6) set.

Packet 26 Processing

One of the uses of packet 26 is to transmit characters

which are not in the basic teletext character set. The family

automatically decodes packet 26 data and, if a character

corresponding to that being transmitted is available in the

character set, automatically writes the appropriate

character code into the correct location in the teletext

memory. This is not a full implementation of the packet 26

specification allowed for in level 2 teletext, and so is often

referred to as level 1.5.

By convention, the packets 26 for a page are transmitted

before the normal packets. To prevent the default

character data over writing the packet 26 data the device

incorporates a mechanism which prevents packet 26 data

from being overwritten. This mechanism is disabled when

the Spanish national option is detected as the Spanish

transmission system sends even parity (i.e. incorrect)

characters in the basic page locations corresponding to

the characters sent via packet 26 and these will not over

write the packet 26 characters anyway. The special

treatment of Spanish national option is prevented if

TXT12. ROM VER R4 is logic 0 or if the TXT8.DISABLE

SPANISH is set.

Packet 26 data is processed regardless of the TXT1. EXT

PKT OFF bit, but setting theTXT1.X26 OFF disables

packet 26 processing.

The TXT8. Packet 26 received bit is set by the hardware

whenever a character is written into the page memory by

the packet 26 decoding hardware. The flag can be reset by

writing a 0 into the SFR bit.

525 WST

The 525 line format is similar to the 625 line format but the

data rate is lower and there are less data bytes per packet

(32 rather than 40). There are still 40 characters per

display row so extra packets are sent each of which

contains the last 8 characters for four rows. These packets

can be identified by looking at the ‘tabulation bit’ (T), which

replaces one of the magazine bits in 525 line teletext.

When an ordinary packet with T = 1 is received, the

decoder puts the data into the four rows starting with that

corresponding to the packet number, but with the 2 LSBs

set to 0. For example, a packet 9 withT=1 (packet X/1/9)

contains data for rows 8, 9, 10 and 11. The error checking

carried out on data from packets with T = 1 depends on the

setting of the TXT1. 8 BIT bit and the error checking control

bits in the page request data and is the same as that

applied to the data written into the same memory location

in the 625 line format.

The rolling time display (the last 8 characters in row 0) is

taken from any packets X/1/1, 2 or 3 received. In parallel

magazine mode only packets in the correct magazine are

used for rolling time. Packet number X/1/0 is ignored.

The tabulation bit is also used with extension packets. The

first 8 data bytes of packet X/1/24 are used to extend the

Fastext prompt row to 40 characters. These characters are

written into whichever part of the memory the packet 24 is

being written into (determined by the ‘X24 Posn’ bit).

Packets X/0/27/0 contain 5 Fastext page links and the link

control byte and are captured, Hamming checked and

stored by in the same way as are packets X/27/0 in 625

line text. Packets X/1/27/0 are not captured.

Because there are only 2 magazine bits in 525 line text,

packets with the magazine bits all set to 0 are referred to

as being in magazine 4. Therefore, the broadcast service

data packet is packet 4/30, rather than packet 8/30. As in

625 line text, the first 20 bytes of packet 4/30 contain

encoded data which is decoded in the same way as that in

packet 8/30. The last 12 bytes of the packet contains half

of the parity encoded status message. Packet 4/0/30

contains the first half of the message and packet 4/1/30

contains the second half. The last 4 bytes of the message

are not written into memory. The first 20 bytes of the each

version of the packet are the same so they are stored

whenever either version of the packet is acquired.

In 525 line text each packet 26 only contains ten 24/18

Hamming encoded data triplets, rather than the 13 found

in 625 line text. The tabulation bit is used as an extra bit

(the MSB) of the designation code, allowing 32 packet 26s

to be transmitted for each page. The last byte of each

packet 26 is ignored.

FASTEXT DETECTION

When a packet 27, designation code 0 is detected,

whether or not it is acquired, the TXT13. FASTEXT bit is

set. If the device is receiving 525 line teletext, a packet

X/0/27/0 is required to set the flag. The flag can be reset

by writing a 0 into the SFR bit.

BROADCAST SERVICE DATA DETECTION

When a packet 8/30 is detected, or a packet 4/30 when the

device is receiving a 525 line transmission, the TXT13.

Packet 8/30. The flag can be reset by writing a 0 into the

SFR bit.

VPS ACQUISITION

When the TXT0. VPS ON bit is set, any VPS data present

on line 16, field 0 of the CVBS signal at the input of the

TDA9554PS Datasheet(PDF) 41 Page - NXP Semiconductors

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