Specifications

CA10 Course Notes
Sharp Electronics (UK) Limited
CE Technical Support Group Page 13
System Control
Resets and oscillators
When the power supply starts up the program within the main microprocessor needs to be reset. This
is achieved with the use of the circuit shown below.
Figure 11 : Reset Operation Circuit
When the STB5V supply has reached its correct level, the output from IC102 changes from a low to a high
level to reset IC101 on pin 67 ( RSTIN ). After IC101 has reset itself it gives a further reset to the audio
processing IC, IC305 via pin 45 ( RESETOUT ). This pin changes from low to high, then back to low and
finally remains high as shown in the diagram below. IC305 is now reset.
Figure 12 : Reset Pulse Timing
Once the main system microprocessor, IC101, has reset and the oscillator is running at the correct
frequency the internal programme sequence is initiated. It first checks that the internal functions of the
IC are working correctly then checks the devices connected to it via the I C bus. If any errors are
2
encountered then the microprocessor will either shut down or produce a fault symptom - see the I C bus
2
line disconnection part of these notes for more details.
When the microprocessor has satisfied itself that all devices connected to it are operating correctly, it will
read information from the EEPROM, IC105, to operate the set in the right sequence.