LC74725 データシートの表示（PDF） - SANYO -> Panasonic

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LC74725

On-Screen Display Controller LSI

SANYO -> Panasonic 

LC74725, 74725M

Note: When closed caption character data is extracted in NTSC-TV mode (MOD0 is high), the control microprocessor can determine whether the current

field is an odd field or an even field by checking the signal level output by the SYNCJDG pin (when SEL0 is high) at the point it detects the rise of the

LN21 signal.

Figure 4 LC74725/M to Decoder LSI (or Microprocessor) Caption Data Transfer Technique 1

(This is the basic usage mode for these LSIs.)

Caption data transfer to the data output buffer is synchronized with the falling edge of the pulse output from LN21. Therefore, the following software

processing is required if the decoder LSI (or microprocessor) does not detect the fall of LN21.

When MOD0 is low, since the data is output to the data buffer once (during the even field) in a single frame, the decoder LSI (or microprocessor) must

perform the transfer control operation at least twice per frame (about 32 ms).

When the transfer control operation is performed twice in the same frame, the second CPDT 16 bits of output data are all zeros. Therefore, the

microprocessor must determine that the data for the next frame had not been transferred to the output buffer in this case.

Note: The LC74725 hardware will not transfer data to the output buffer while CS2 is low. Therefore the decoder LSI (or microprocessor) must restore CS2

from the low level to the high level after completing a data transfer control cycle.

This transfer technique (technique 2) cannot be used in NTSC-TV mode, i.e., when MOD0 is high.

Figure 5 LC74725/M to Decoder LSI (or Microprocessor) Caption Data Transfer Technique 2

(When a port to detect the fall of LN21 cannot be allocated in the decoder LSI (or Microprocessor).)

No. 5213-6/16

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