AK8858 Datasheet, PDF (59/96 Pages) Asahi Kasei Microsystems – PS/SD Multi Format Video Decoder

[AK8858]
[7.30] VBI information decoding
The AK8858 decodes closed-caption, closed-caption-extended, VBID(CGMS), and WSS signals on the vertical
blanking signal, and writes the decoded data into a storage register. The AK8858 reads each data bit in
Request VBI Information register (Sub Address 0x1A [3:0]) as a decoding request and thereupon enters a data
wait state. Data detection and decoding to the storage register are then performed which indicates the
presence or absence of data at STATUS 2 register (Sub Address 0x23 [3:0]) for host. The host can therefore
determine the stored values by reading the respective storage registers. The value in each storage register is
retained until a new value is written in by data renewal. For VBID data (CGMS-A), the CRCC code is decoded
and only the arithmetic result is stored in the register.
Signal
Closed Caption
Closed Caption Extended Data
VBID
WSS
Line Number
Line21
Line284
Line20 / 283
Line20 / 333
Line41
Line23
Line43
Following are store registers. (Sub Address: 0x26 ~ 0x2D)
Closed Caption 1 Register, Closed Caption 2 Register, WSS 1 Register, WSS 2 Register,
Extended Data 1 Register, Extended Data 2 Register, VBID 1 Register and VBID 2 Register
Notes
525i
525i
525i
625i
525p
625i
625p
Reading data flow chart
START
[Request VBI Information Register]
xxRQ-bit = 1
(Decode request)
[Status 2 Register] Read
(Confirm decode ending)
No
Request bit
=1?
YES
Data Register
Reading
END
MS1230-E-00
- 59 -
2010/9