MCU pull-up resistor

Because there is no pull-up resistor inside the P0 port, it is open-drain, no matter how big the driving capability is, it is equivalent to it has no power supply, and needs external circuit supply. In most cases, the P0 port is necessary to add Resistance. 1. The P0 port of the general 51 MCU is not connected to the pull-up resistor when it is used as address/data multiplexing. 2. When used as a general I/O port, since there is no pull-up resistor inside, connect the pull-up resistor! ! 3. When the p0 port is used to drive the PNP tube, the pull-up resistor is not needed because the low level is effective at this time; 4. When the P0 port is used to drive the NPN tube, the pull-up resistor is needed because At this time, only when P0 is 1, the latter end can be turned on. To put it simply, it must have a power supply to drive the LCD display. Otherwise, it will not light up, and there is no power supply at the P0 port. Therefore, an external power supply is required, and the resistor is connected to limit current. P2 and P3 ports do not need external power supply and resistors.

Pull-up Resistor Definition: Pull-up is to clamp an indeterminate signal through a resistor at a high level! The resistor acts as a current limiting device at the same time! Pull down the same reason! Pull-up is to inject current into the device, pull-down is output current; weak strength is only the resistance of the pull-up resistor is different, there is no strict distinction; for non-collector (or drain) open-circuit output type circuit (such as ordinary gate circuit) to boost current The ability of the voltage and the voltage is limited. The function of the pull-up resistor is mainly to output the current channel for the open-collector output type circuit.

Pull-up: When 1TTL drives CMOS, if the TTL output is at the lowest level lower than the CMOS minimum level, increase the output high level. 2 OC gate must be pulled to increase the level value by 3. The drive capability of the output (common to the MCU) 4 CMOS chip (especially the chip of the gate), for anti-static interference, the unused pins are not suspended, generally pull up, reduce the impedance, provide the discharge path 5, increase the output level Improve the noise margin of the chip input signal, enhance the anti-jamming 6. Improve the bus's anti-electromagnetic capability, and the empty leg is susceptible to electromagnetic interference. 7 Long-line transmission plus pull is the principle of impedance matching to suppress reflection interference: 1 from saving power and chip Current, capacity should be as large as possible, R is large, I is small 2 from ensuring the driving ability, the resistance should be small enough, R is small, I is big 3 pairs of high-speed circuits, plus pulling may be gentle on the edge (rise time is extended) Choose between 1K---10K (according to the actual situation)