1. The difference between asynchronous and synchronous is whether there is a unified clock signal
Asynchronous No Synchronous Yes
RS485 half-duplex, asynchronous, serial, differential input------Multi-level communication (USB\keyboard and other peripherals)
RS232 full-duplex, asynchronous, serial, single-ended input------one-to-one communication
2. The difference between combinational logic circuit and sequential logic circuit
Combination: the output at any moment depends only on the input at that moment, and has nothing to do with the original state of the circuit
Timing: not only depends on the current input signal, but also depends on the original state of the circuit, or in other words, it is also related to the previous input
| left combinatorial logic circuit right clock logic circuit |
Encoder decoder data selector adder Numerical Comparator |
Latches trigger register Shift Register memory |
Three, OC, OD, three-state gate
OC: Line AND, output higher voltage (used as LED drive, analog conversion, motor drive)
The relationship between input and output
- Low level (0) ----------- 0
- High level (1) -----------high impedance state
- High resistance state ------------------ High resistance state
OD: The output can be switched between high and low
- Low level (0) ----------- 0
- High level (1) -----------high impedance state
- High-impedance state -------------------0
Tri-state gate: used in bidirectional I/O circuits and shared bus structures.
- Low level (0) ----------- 0 (as of)
- High level (1) -----------1 (conduction)
- High resistance state ------------------- High resistance state
4. Trigger
type of trigger features input logical expression SR flip-flop 01 is set to 0, 10 is set to 1, 00 is kept, 11 is forbidden Input at both ends Q ∗ = S + R ′ Q JK flip-flop 01 set 0, 10 set 1, 00 keep, 11 negate Input at both ends Q ∗ = J Q ′ + K ′Q D flip flop output equals input single-ended input Q ∗ =D T flip flop 0 keep, 1 negate single-ended input Q ∗ = T Q ′ + T ′ Q
Five, Schmitt trigger
It is characterized by the ability to shape the signal into a rectangular pulse. The Schmitt trigger can improve the anti-interference ability of the circuit .
6. Comparator
Voltage comparator, zero-crossing comparator, hysteresis comparator
Hysteresis comparators are usually called "Schmitt trigger comparators" or " hysteresis comparators" and have strong anti-interference ability . ,
The method of judging the working area of the op amp is:
If there is negative feedback, it works in the linear region;
If there is positive feedback or no feedback, it works in the nonlinear region;
7. Diodes
Switch---------one-way conductivity ("on" in the saturation region, "off" in the cut-off region)
Voltage regulation --------- reverse breakdown characteristics
Conduction condition: forward voltage > reverse voltage;
Internal conditions: more doping, thinner N region; multi-carrier diffusion, few-carrier drift
Temperature ↑----increased reverse current
Temperature ↓----Reverse current decreases
