Caption Data Transfer from the LC7455A/M to the Decoder IC (microcontroller): Method 2

(For applications that cannot provide an input port on the decoder IC (microcontroller) to detect LN21 falling edges.)

In modes 1 and 2, since data is output to the output buffer once every frame (in the even field), the decoder IC (microcontroller) must perform a transfer control operation at least twice every frame (about 32 ms).

When the second control operation is performed in a given frame, the CPDT output for that second operation will be 16 bits of zeros. This allows the microprocessor to recognize that the data for the next frame has not yet been

transferred to the output buffer.

Notes: When CE remains low, the hardware will not transfer the data to the output buffer. Thus applications must restore CE from low to high after each data transfer to the decoder IC (microcontroller) operation has completed.

This transfer technique (method 2) cannot be used in modes 3 and 4.

Within a single frame (modes 1 and 2)

16 bits of data all

of which are zeros.

16 bits transfered