STB5701 datasheet(25/35 Pages) STMICROELECTRONICS

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STB5701

Functional description

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4.5

Start code detection example

This section explains the operation of the start code detector with reference to the start code

sequence illustrated in the following figure:

Figure 8.

START code

Firstly we assume the nominal symbol duration is 500 µs, in this example there are then

13 symbol (denoted as 12 to 0 in the figure above).

If the device is operating from a 27 Mhz external clock then we program the prescaler to 27.

The internal sampling clock will be 1Mhz and the sampling resolution will be 1us. To add

some error tolerance we also program an upper and lower bound on the symbol duration as

well as the nominal value. In this case 400 (corresponding to 400us) in

SCD_symbol_min_time register, 500 (corresponding to 500us) in SCD_symbol_nom_time

and 600 (corresponding to 600us) in SCD_symbol_max_time.

Now we program 0b1001111001111 into the SCD_code register and 13 (0x0d)

corresponding to 13 symbols to be detected into the SCD_code_length register. The start

code detection is started by setting the enable and research bits in SCD_config register to

‘1’.

The start code detector checks for the minimum symbol time of each symbol and the

sequence in which symbols are received. If the symbol time is not respected by the input

(incase of noise) the start code detection is re-initialized.

The detector is capable of simultaneously searching for two different start codes, the

alternative code is written into the upper 16 bits of SCD_code register.

500 µs

1 ms

2 ms

STB5701 Datasheet(PDF) 25 Page - STMicroelectronics