عمل الميكروكمبيوتر .. كتاب التلفزيون الملون والعادي

9-19 Microcomputer work:

A microcomputer is an integrated computer that receives new information and processes it intelligently with the information and instructions programmed on it. It drives and adjusts the receiving television set and is designed to include the following features:

1- The device does not require re-tuning if it is moved from one city to another.

2 - No additional source of programming power is required, electricity or batteries.

3 - Channel tuning is done directly or electronically, to search for the working channel
The highest or lowest (Seekoff) (Seekon)

4 - Fine tuning (AFT) circuit that compensates for frequency errors in a range
Rom.

E - The possibility of fine tuning manually for all channels. And a memory to memorize the last channel number. The simplified diagram, Figure (19-14), shows the entrances and exits of the microcomputer. Its control system performs a continuous scanning process for all the entrances and performs computer operations based on the instructions stored in it in the memory (Rom), and the computer program is contained in the metallic part of an integrated circuit (IC), and so on, it does not need Standby accumulators or batteries when the original power is cut off. There are (629) steps in the program that occupies (629) positions in the memory of its capabilities (867), and the portion of the memory is used for routine self-sensing (VHF) channels.

The microcomputer scans the keyboard (195 times per second). It examines the positions of the Seek and Fine Tune switches and compressors, inspecting new control signals, and feels the closure of the SEEK switch - the fine tuning switch and compressors from 0 to 9. The channel switch up and down - Channel down, Channel up, and receives input signals from presence or presence sensing circuits. The absence of the station signal and the accuracy of the device tuning .. When we select a new channel and enter its number, the microcomputer gives the correct information in binary to the voter oscillator and the frequency divider of the reference oscillator (LED) and determines whether the new channel
​​​​​​In the low or high VHF range or in the UHF range, the correct output +B applies to the VHF and UHF ranges, and the (sleep - volume) switch, and all these functions are done in real time.

If the automatic search and fine tuning (SEEK) switch is in the working state when tuning in to a new channel - the input from the sensing circuit indicates the presence or absence of a station signal. If the signal is present, the sensitivity circuit indicates the accuracy of the tuning.

The microcomputer processes this information as follows:

​​​​1 - If the new channel is in the VHF range and the sensor input to the microcomputer indicates that there is no signal, then the microcomputer starts to search locally 5.1 to MH2.5. If it is not tuned to a station within the specified time, the system will advance to the next channel and repeat the same the operation . The program gives (300 milliseconds) to determine the existence of a station and (328) milliseconds (seconds) in addition to performing a local search.The (AFT) compensates for the frequency error of the system - this function is specified in the (VHF) range, but the next channel search function is in In the absence of a station signal, it applies to both the VHF and UHF bands

2 - When the search switch is in the (SEEKOFF) state, the microcomputer ignores the sensor inputs - thus, the device tunes exactly to the correct frequency for the required channel. It stays on this channel whether there is a signal or not, allowing the use of a VTR or game console. In this mode, the viewer can fine-tune manually, by setting the fine-tuning switch to (Normal) and adjusting one of the fine-tuning controls to up (or down)

3 - SEEK UP or DOWN to advance to the next channel. We press the Up or Down button, which assigns the correct number of the next channel to the frequency divider assembly of the voter oscillator. This results in unequal inputs to the PLL comparator circuit, which changes the channel by shifting the tuning voltage.

4. Automatic or manual fine tuning is done by changing the binary input of the digital to the reference oscillator section. Thus the reference frequency in the comparator increases or decreases, and this produces a proportional change in the tuning voltage which in turn changes the frequency of the voter oscillator appropriately - and when the required fine-tuning is corrected the reference oscillator maintains the tuning position with the accuracy and stability of the crystal oscillator.