Explain Digital clock with block Diagram
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Logic-Design---10CS33-VTU-notes10CS33-->View question

Explain Digital clock with block Diagram

Digital clock


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Picture of Block Diagram
Untitled Diagram.jpg

To avoid cramping up space, the alarm module is given a separate block diagram. The working of the block diagram is explained in detail here. Parts of this section might seem like the repetition of he logic of the circuit discussed before, but bear with me.

A 1 Hz (signal at every 1 second interval) square wave from an astable multivibrator is applied as clock signal to the S0 counter which counts from 0 to 9 after every second. After 9, the values reset back to 0. Whenever S0 (4 bits) becomes 0000, a clock signal has to be generated. This clock signal is applied to S1 counter which counts from 0 to 5. After it reaches 5 and S0 becomes 9, the next pulse will make both S1 & S0 zero.

When S1 (3 bits) becomes 000, a clock is generated and applied onto M0. This is extended to M1 just like S1. And similar to S1 when M1 (also 3 bits) becomes 000, a clock pulse is applied to HH. HH is a 4 bit counter counting from 1 - 12. Here everytime HH becomes 12, a clock pulse if used to toggle A to P or P to A.

Each S0, S1, M0 & M1 counter's data is converted to 7 segment display format and applied to a 7 segment display. HH requires a Binary to BCD (Binary Coded Decimals) converter. So, the 7 segment displays show the time as it is stored in the flip-flops.

The alarm module uses an 8 bit comparator to accept the use defined time. As explained earlier, the first 4 bits are dedicated to HH, the next 3 bits are M1 and the last bit is to accept A/P. This 8 bit data is denoted A. The input from the dip switch is given to the comparator. The corresponding bits of data are also applied from the flip-flops. The loic is that whn the time as counted b te flip-lops is the same as that of the dip switch, the comparator's A=B will become 1. This is used to toggle another lip-flop (its dedicated to this function alone) which is connected to the alarm. So, when A = B, the alarm sounds and it keeps sounding until the flip-flop is manually reset to 0.

Some of you might think, we can set the alarm only for times like 4: 30, 4:40 and during these times the A = B will be '1' for 10 minutes. For example, if we set te alarm for 4: 30 PM, then the comparator output A = B will be 1 for 4:30 PM to 4: 39 PM because only M1 values are compared and M1 values are same.


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