Datasheet

2−4
At powerup the host interface is required to program the VDP-configuration RAM (VDP-CRAM) contents with the
lookup table (see Section 2.20.58). This is done through port address C3h. Each read from or write to this address
will auto increment an internal counter to the next RAM location. To access the VDP-CRAM, the line mode registers
(D0h−FCh) must be programmed with FFh to avoid a conflict with the internal microprocessor and the VDP in both
writing and reading. Full field mode must also be disabled.
Available VBI lines are from line 6 to line 27 of both field 1 and field 2. Each line can be any VBI mode.
Output data is available either through the VBI-FIFO (B0h) or through dedicated registers at 90h−AFh, both of which
are available through the I
2
C port.
2.9 VBI FIFO and Ancillary Data in Video Stream
Sliced VBI data can be output as ancillary data in the video stream in the ITU-R BT.656 mode. VBI data is output during
the horizontal blanking period following the line from which the data was retrieved. Table 2−2 shows the header format
and sequence of the ancillary data inserted into the video stream. This format is also used to store any VBI data into
the FIFO. The size of FIFO is 512 bytes. Therefore, the FIFO can store up to 11 lines of teletext data with the NTSC
NABTS standard.
Table 2−2. Ancillary Data Format and Sequence
BYTE
NO.
D7
(MSB)
D6 D5 D4 D3 D2 D1 D0
(LSB)
DESCRIPTION
0 0 0 0 0 0 0 0 0
Ancillary data preamble
1 1 1 1 1 1 1 1 1
Ancillary data preamble
2 1 1 1 1 1 1 1 1
3 NEP EP 0 1 0 DID2 DID1 DID0 Data ID (DID)
4 NEP EP F5 F4 F3 F2 F1 F0 Secondary data ID (SDID)
5 NEP EP N5 N4 N3 N2 N1 N0 Number of 32 bit data (NN)
6 Video line # [7:0] Internal data ID0 (IDID0)
7 0 0 0 Data
error
Match
#1
Match
#2
Video line # [9:8] Internal data ID1 (IDID1)
8 1. Data Data byte
1
st
word
9 2. Data Data byte
1 word
10 3. Data Data byte
11 4. Data Data byte
: : :
m−1. Data Data byte
N
th
word
m. Data Data byte
N word
NEP EP CS[5:0] Check sum
4(N+2)−1 1 0 0 0 0 0 0 0 Fill byte
EP: Even parity for D0−D5 NEP: Negated even parity
DID: 91h: Sliced data of VBI lines of first field
53h: Sliced data of line 24 to end of first field
55h: Sliced data of VBI lines of second field
97h: Sliced data of line 24 to end of second field
SDID: This field holds the data format taken from the line mode register of the corresponding line.
NN: Number of Dwords beginning with byte 8 through 4(N+2). This value is the number of Dwords where
each Dword is 4 bytes.
IDID0: Transaction video line number [7:0]