CS4954 datasheet(23/56 Pages) CIRRUS

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CS4954 CS4955

DS278PP4

H-sync can be delayed by a full line, in 74 nsec in-

tervals.

V-sync can be shifted in both directions in time.

The default values are 18 and 23 for NTSC and

PAL respectively. Since the V-sync register is 5

bits wide (Sync Register 0), the V-sync pulse can

be shifted by 31 lines in total.

V-sync can preceed by a maximum of 18 lines

(NTSC) or 23 lines (PAL) respectively from its de-

fault location, and V-sync can follow by a maxi-

mum of 13 lines (NTSC) or 8 lines (PAL) from its

default location.

5.10. Wide Screen Signaling (WSS) and

CGMS

Wide screen signaling support is provided for

NTSC and for PAL standards. Wide screen signal-

ing is currently used in most countries with 625 line

systems as well as in Japan for EDTV-II applica-

tions. For complete description of WSS standard,

please refer to ITU-R BT.1119 (625 line system)

and to EIAJ CPX1204 for the Japanese 525 line

system.

The wide screen signal is transferred in a blanking

line of each video field (NTSC: lines 20 and 283,

PAL: lines 23 and 336). Wide screen signaling is

enabled by setting WW_23 to “1”. Some countries

with PAL standard don’t use line 336 for wide

screen signaling (they use only line 23), therefore

we provide another enable bit (WSS_22) for that

particular line.

There are 3 registers dedicated to contain the trans-

mitted WSS bits (WSS_REG_0, WSS_REG_1,

WSS_REG_2). The data insertion into the appro-

priate lines are performed automatically by this de-

vice. The run-in and start code bits do not have to

be loaded into this device, it automatically inserts

the correct code at the beginning of transfer.

5.11. Teletext Support

This chip supports several teletext standards, like

European teletext, NABTS (North American tele-

text), and WST (World Standard Teletext) for

NTSC and PAL.

All these teletext standards are defined in the ITU-

R BT.653-2 document. The European teletext is

defined as “teletext system B” for 625/50 Hz TV

systems. NABTS teletext is defined as “teletext

system C” for 525/60 Hz TV systems. WST for

PAL is defined as “teletext system D” for

624/50 Hz TV systems and WST for NTSC is de-

fined as “teletext system D” for 525/60 Hz TV

systems.

This chip provides independant teletext encoding

into composite 1, composite 2 and s-video signals.

The teletext encoding into these various signals is

software programmable.

In teletext pulsation mode, (TTX_WINDOW=0),

teletext bitstream sampled at the 27 Mhz clock. At

each rising edge of the TTXRQ output signal a sin-

gle teletext bit has to be provided after a program-

mable input delay at the TTXDAT input pin.

Phase variant interpolation is achieved on this bit-

stream in the internal teletext encoder, providing

sufficient small phase jitter on the ouput text lines.

TTXRQ provides a fully programmable request

signal to the teletext source, indicating the insertion

period of the bitstream at indepenantly selectable

lines for both TV fields. The internal insertion win-

dow for text is set to either 360, 296 or 288 teletext

bits, depending on the selected teletext standard.

The clock run-in is included in this window.

Teletext in enabled by setting the TTX_EN bit to

“1”. The TTX_WST bit in conjunction with the

TV_FORMAT register select one of the 4 possible

teletext encoding possibilities.

The teletext timing is shown in the Figure 12.

TTXHS and TTXHD are user programmable and

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