z86131 ZiLOG Semiconductor, z86131 Datasheet - Page 39

• Manufacturer Part Number: z86131
• Description: Ntsc Line 21 Decoder
• Manufacturer: ZiLOG Semiconductor

ZiLOG
Filtered XDS Data Format
Filtered XDS data is output from the Z86129/130/131 in the
order it is received on Line 21. In other words, think of the
Z86129/130/131 XDS filter function as creating a new,
smaller stream of XDS data packets. This new data stream
looks exactly as though the Class and Type specified in the
XDS Filter Register (05h) are
21 of field 2. The filtered data output from the Z86129/131
is in full compliance with EIA–608 specifications for XDS
data streams; headers and control codes intact. See Note
paragraph in the next column for a special exception to this
rule.
XDS data and header information (including START,
CONTINUE, and END commands) are passed through the
filter for the XDS class and type specified in the XDS Filter
Register. All other Line 21 data is filtered out and is not out-
put or used to generate a Data Available Flag (DAV) in the
Serial Status Register.
T o p r o p e r l y r e a d f i l t e r e d X D S d a t a f r o m t h e
Z86129/130/131, the master device must first write the
XDS Filter Register (05h) with its desired XDS Class and
DS007200-TVX0199
{Write
COMMAND,
Filter Code}
{C5,41}
{C5,61}
{C5,1F}
{C5,01}
{C5,28}
{C5,9F}
Table 23. XDS Data ExtractionÑ
Example Filter Settings
XDS Filter Output
All In Band, Current Class packets
recovered.
Program Rating, Current Class packets
recovered. This Filter May be Used for V-
Chip Data Packet Recovery.
All XDS packets recovered.
All Current Class packets recovered.
Time information recovered. This Þlter
extracts the Time of Day (TOD) and
Local Time Zone (LTZ) packets from the
Miscellaneous Class data.
This Þlter may be used to implement
Auto Clock-Setting in TVs and VCRs.
VCR Information recovered. Selects
TOD, LTZ, Net ID, Local Call Letters,
Impulse Capture, Tape Delay, Composite
2 and Out of Band Channel Number
packets for recovery.
the only data
encoded on Line
P R E L I M I N A R Y
Type information. For example, in Z86129/130, in order to
extract ONLY the Line 21 Program Rating information, the
master must write the value 61h to the XDS Filter Register.
The master should then poll the state of the DAV bit in the
SSR until DAV = 1.
As soon as DAV = 1, the master may initiate a 3-byte read
in the normal manner (XDS data bytes always arrive in
pairs, so it is safe to assume that RD2=1 when DAV=1 in
the SSB). A 3-byte read always yields two data bytes, which
in this case are the first two bytes of the Current Class, Pro-
gram Rating Type XDS data stream encountered on Line21
field 2. The master device must then interpret those two
bytes according to EIA–608 specifications for Current
Class, Program Rating Type data. Refer to EIA–608 for data
formats.
The XDS filters on the Z86129/130/131 greatly reduce the
amount of field 2 data passed on to the master device for
further processing and interpretation. However, the master
device must still interpret the filtered data stream in accor-
dance with EIA–608. The filtered data stream from the
Z86129/131 is in full compliance with EIA–608. In other
words, the filtered data stream contains all the XDS com-
mand and data packets, in standard EIA–608 format, but
only for the selected XDS Class and Type(s).
Note: The Z86129/130 XDS filter for Program Rating infor-
m a t i o n b e h a v e s d i f f e r e n t l y t h a n a l l o t h e r
Z86129/130/131 predefined XDS filters. This change
has been made to minimize the amount of data passed
through the Program Rating XDS filter, thereby mini-
mizing the interpretation and communications load on
the master device. When the XDS Filter Register is set to
61h (Class=01h (Current), Type=05h (Program Rating)
the only data from Line 21 field 2 that passes through the
filter is:
1. Program Rating Packet: [xxh,xxh]. The Current Class
Program Rating data byte pair as defined in EIA–608.
The program’s rating is encoded per EIA–608 in the xxh
byte pair.
2 The END Packet [0Fh,CHKSUM]. A two-byte packet
that includes a CHKSUM computed per EIA–608. The
checksum calculation includes the START packet
[01h,05h] even though this value was not passed through
the filter.
NTSC Line 21 Decoder
Z86129/130/131
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