The boot-up sequence
Normally, a STB is never switched off. When not in use, it remains in the standby mode. Its microprocessor, microcontroller and all other processing chips remain set and ready to receive and process data.
However, when an STB is switched on from cold, the reset pin of the microprocessor goes high and the microprocessor searches for the start-up program by placing the start-up address on the address bus. This address is the start of the start-up routine stored in flash memory. The processor then goes through a comparatively lengthy process of setting, initialising, configuring and programming the processor and decoder chips as described in Chapter 16.
When the initialisation process is completed successfully, the channel decoder begins to search for the default channel, known as the home chan- nel. If the signal is detected, the channel decoder locks to it; data is received, decoded and processed. Picture and sound are produced. If the home channel cannot be detected, the channel decoder searches for other channels. Failure to lock to any incoming signal is indicated by a ‘no signal’ message on the screen.
