Z86131 datasheet(32/50 Pages) ZILOG

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Z86129/130/131

NTSC Line 21 Decoder

P R E L I M I N A R Y

DS96TEL0200

INTERNAL REGISTERS (Continued)

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

be output, or used to generate a data available flag (DAV)

in the Serial Status Register.

properly

read

filtered

XDS

data

from

the

Z86129/130/131, the master device must first write the

XDS Filter Register (05h) with its desired XDS Class and

Type information. For example, 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 will be the first two bytes of the Current

Class,

Program

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

accordance with EIA-608. The filtered data stream from

the Z86129/130/131 will be in full compliance with EIA-

608. In other words, the filtered data stream will contain all

the XDS command 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

information behaves differently than all other Z86129/130

predefined XDS filters. This change has been made to

minimize the amount of data passed through the Program

Rating XDS filter, thereby minimizing 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 will pass through the filter is:

Program Rating Packet: [xxh,00h]. The Current Class

Program Rating data byte pair as defined in EIA-608.

The program’s rating is encoded per EIA-608 in the

byte xxh.

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.

Z86131 Datasheet(PDF) 32 Page - Zilog, Inc.

Z86131 Datasheet(HTML) 32 Page - Zilog, Inc.

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