1, TTL level: output high> 2.4V, output low level <0.4V. At room temperature, the high output high is 3.5V, and the output low is 0.2V. Minimum input high and low level: input high> = 2.0V, enter low level <= 0.8V, noise tolerance is 0.4V. 2, CMOS level: 1 Logic level voltage is close to the power supply voltage, 0 logic level close to 0V. And have a wide noise tolerance. 3. Level conversion circuit: Because the value of TTL and COMS is different (TTL 5V <==> CMOS 3.3V), it is necessary to conversion when connecting to each other: Pressing, there is no deep thing. Haha 4, OC door, ie the collector open road gate circuit, OD door, the drain open road gate circuit, the external pull-up resistor and power supply can be used as a high and low level. Otherwise it is generally only used as a large voltage and a large current load, so it is called the driver circuit. 5, TTL and COMS circuit comparison: 1) The TTL circuit is a current control device, and the COMS circuit is a voltage control device. 2) The speed of the TTL circuit is fast, and the transmission delay is short (5-10ns), but power consumption is large. The COMS circuit is slow, the transmission delay is long (25-50ns), but the power consumption is low. The power consumption of the COMS circuit itself is related to the pulse frequency of the input signal. The higher the frequency, the chipset is hot, which is a normal phenomenon. 3) Locking effect of the COMS circuit: The COMS circuit has increased dramatically due to the incoming current, and the internal current increases, unless the power is turned off, the current is increasing. This effect is the locking effect. When a locking effect is generated, the internal current of the COMS can reach 40 mA, which is easy to burn the chip. Defense measures: 1) add a clamp circuit on the input and output to make the input and output do not exceed the specified voltage. 2) The power input of the chip adds a coupling circuit to prevent the VDD terminal from instantaneous high pressure. 3) Plit the current resistance between VDD and external power, even if there is a large current, do not let it go. 4) When the system is powered by several power supplies, the switch is in order: On the next order, turn on the COMS circuit to get the power supply, then turn on the input signal and load; turn off the input signal and load, then Turn off the power of the COMS circuit. 6. Precautions for the COMS circuit 1) COMS circuit When voltage control device, its input is very large, and the capture capacity of the interference signal is very strong. Therefore, do not have to be suspended, to connect the upper pull resistor or pull-down resistor to give it a constant level. 2) When the input terminal is connected to the source of the internal group, the limit current resistor is required between the input and the signal source, so that the input current is limited to 1 mA. 3) When the signal transmission line is connected, the matching resistor is connected to the COMS circuit. 4) When the input is connected, the resistor should be indirectly protected at the input and capacitance. The resistance value is R = V0 / 1m.v0 is the voltage on the external capacitor. 5) The input current of the COMS exceeds 1 mA, it is possible to burn the COMS.
7. Input end load characteristics in the TTL gate circuit (processing of special circumstances for refractive resistance): 1) When the floating is equal to the input terminal. Because it can be seen as an infinite resistor. 2) When the gate circuit input is 10K, then the low level is input, and the input end is presented high rather than a low level. Since the input end load characteristics of the TTL door circuit can be seen that the low level signal it enters only by the gate circuit, the series resistance is rendered by the series resistance. High level. This must pay attention. The COMS door circuit does not have to consider these. 8. TTL circuit has a collector opening OC door, MOS tube also has an OD door of the drain open circuit corresponding to the collector, and its output is called open drain output. The OC door has a leakage current output during the hour, which is a leakage current, why is there a leakage current? That is because when the three-machine tube is cut off, its base current is about 0, but is not true 0, the current of the collector of the triode is not true 0, but about 0. And this is a leakage current. Open and drain output: The output of the OC door is an open drain output; the output of the OD door is also an open drain output. It can absorb a large current, but the current cannot be output outward. Therefore, in order to enable input and output current, it is useful to use the power supply and pull-up resistance. The OD gate is generally used as an output buffer / drive, the level converter, and the need to satisfy the absorption large load current. 9, what is Totem pillar, what is the difference from the opening and leakage circuit? In the TTL integrated circuit, the output is called the output of the pull-up three pole called the Totem column output, and no OC door is called. Because TTL is a three level, the totem column is also two three-level pipe push-pull. Therefore, the push is Totem. General totem output, high level 400ua, low level 8mA transferred from: http://blog.21ic.com/more.asp? Name = yzy1102 & id = 7688
