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SAA7115_Datasheet.fm
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page 67
Last edited by H. Lambers
Philips Semiconductors
CS-PD Hamburg
CVIP2
Datasheet
SAA7115
Date:
10/23/01
Version:
0.67
8.4.2
I
2
C R
EADBACK OF SLICED
VBI
DATA
The I
2
C Readback unit offers readback for the following VBI data standards via the I
2
C bus (subaddresses 66H 7FH):
60Hz / 525 lines VBI data standards
– US Closed Caption (CC525):
1 byte header + 2 x 2 bytes payload
– Copy Generation Management System (CGMS, US Wide Screen Signalling (WSS525)):
1 byte header + 2 x 3 bytes payload
– Gemstar1x:
1 byte header + 2 x 2 bytes payload
– Gemstar2x:
1 byte header + 2 x 4 bytes payload
50Hz / 625 lines VBI data standards
– European Closed Caption (CC625):
1 byte header + 2 x 2 bytes payload
– European Wide Screen Signalling (WSS625, majority decoded and be-phase decoded):
1 byte header + 2 x 2 bytes payload
For each VBI data standard the amount of data of one frame (one line per field) and a one byte header can be stored.
The I2C Readback registers for Wide Screen Signalling and Closed Caption are shared for 60Hz / 525 lines VBI data
standards and 50Hz / 625 lines VBI data standards. In case of decoding WSS625 this data is sore to the same registers
than decoded WSS525 data with the third payload byte of each line left unconsidered.
The one byte header delivers decoding error status and the current update status separately for each field as well as a
free running 4 bit field counter as reference information, to be able to detect multiple read data or loss of data (refer to
table 20)
Table 20
Structure of the I
2
C readback header
The I2C Readback unit guarantees consistency between header information and sliced data using internal
mirror-registers for the sliced data, which updated at the same time the header is accessed for reading via the I
2
C bus.
I.e. The I
2
C Readback header must be always accessed before getting the latest data. In case the sliced data has been
read already or is being updated at the time the header is accessed for reading, this will be signalled in the header bits
7 and 5 for each field separately.
Additionally to the read access to the header the data coming from VBI data slicer is copied into one of the mirror registers
only, if the following additional conditions are satisfied:
The data type as set in the LCR register must equal to the one of the sampled data.
The data must be indicated as valid data.
The maximum number of data bytes per line (CC, WSS625, Gemstar1x:2, CGMS:3, Gemstar2x: 4) is not exceeded
BIT
HEADER DESCRIPTION
7
6
5
4
data of odd field (field_id = 0) is incomplete, i.e. not updated since last read, if set.
one or more data bytes of odd field (field_id = 0) are erroneous (data valid signal became inactive), if set.
data of even field (field_id = 1) is incomplete. i.e. not updated since last read, if set.
one or more data bytes of even field (field_id = 1) are erroneous (data valid signal became inactive), if set.
field_count (counts up, field identifier represents the LSB)
3:1