bt865a Conexant Systems, Inc., bt865a Datasheet - Page 37

• Manufacturer Part Number: bt865a
• Description: Ycrcb To Ntsc/pal Digital Video Encoder
• Manufacturer: Conexant Systems, Inc.

Bt864A/Bt865A Data Sheet
1.9.1
1.9.2
1.9.3
Figure 1-20. PQ Ratio Counter
100138C
02/17/03
CCIR601 Operation (13.5 MHz pixel rate)
Square Pixel Operation (14.75 MHz pixel rate)
Teletext Clock Generation
The bit duration follows this pattern which repeats every 37 teletext bits. Each teletext data
bit is carried by four CLKs except bits 10, 19, 28, and 37 which are three CLKs in
duration. This pattern continues until all 360 bits (1402 CLKs) have been transferred.
This bit pattern repeats after every 111 teletext bits: After every teletext bit that is carried
by five CLKs the next three teletext bits are carried by four CLKs except for the first bit of
the pattern which is five CLKs in duration and only the next two bits are carried by four
CLKs. This pattern continues until all 360 bits (1531 CLKs) have been transferred. The
repeating bit duration pattern starting at bit 1 would be:
Figure 1-20
shifting out the teletext data serially to the Bt864A/Bt865A. The diagram is for
illustrative purposes only. The actual implementation is left to the user.
Table 1-6. Teletext Clock P and Q Values
P
Bit number:
Duration in
CLKs:
29.5 MHz
27 MHz
CLK
A
B
shows how to generate a teletext clock using a P:Q ratio counter for
ADDER
CO
CLK
SUM
1 2 3 4 5 6 7 8 9
5 4 4 5 4 4 4 5 4
Conexant
D
Pixel Rate
14.75 MHz
CLK
13.5 MHz
Q
ENABLE_TTX_CLK
Teletext Clock
REGISTER
MODULO
RSTN
Q
10
111
4
37
P
11
4
12
100138_021
5
13
4
Circuit Description
144
472
Q
14
4
15...
4...
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