Password control circuit of alarm device

In some important departments or warehouses, alarm devices are often installed to prevent outsiders from illegally entering. Figure 4-6-3(a) shows the system block diagram of an alarm device.

Figure 4-6-3 Password alarm system

Figure 4-6-3(b) is the schematic diagram of the password control circuit.

The password control unit has many input and output signals, which are not easy to describe using a state diagram (table). However, a waveform diagram can be drawn based on the next state equation and output equation to understand its working process.

Next-state equations of each flip-flop

Q0n+1 = PRAM.Q1nQ0n + (CNT=4 + BT)Q1nQ0n + BT.EQ.Q1nQ0n

Q0n+1 = PRAM.SEC. Q1nQ0n + (CNT=4 + BT + EQ)Q1nQ0n

And the output equation of the circuit

CR = Q1Q0

WR = BT . Q1Q0

SEC_ON =  Q1Q0

ALARM =  Q1Q0

Figure 4-6-4(a) shows the timing waveform of the input and output signals of the control unit during the password setting process.

Figure 4-6-4 Timing waveform of the controller

Figure 4-6-4(b) shows the timing waveforms of the control unit's related signals when the circuit is in the alert state.

Figure 4-6-4 Timing waveform of the controller