Shulou(Shulou.com)06/01 Report--

Last lesson we mentioned a kind of "quasi-two-way IO" external structure of the single-chip microcomputer IO port. In practice, our single-chip microcomputer IO port has three other forms, which can be distinguished as open-leak, push-pull, and high resistance. We analyze the other three forms through figure 9-1.

Fig. 9-1 IO configuration diagram of single-chip microcomputer

Before our complex introduction to the "quasi-two-way IO", we are using a transistor to clarify, out of a rigorous position, we here according to the practice situation with the MOS tube drawing. In practice, the transistor is conducted by current, while the MOS tube is conducted by voltage, the detailed notice has something to do with their external structure, here we do not need to care for the time being, if you need to understand in the future, you can directly find and imitate e-books or Baidu related materials to stop studying too carefully. In the single-chip microcomputer IO port shape of this piece of content, we can take the MOS tube as a transistor to understand. In figure 9-1, T1 is equivalent to a PNP transistor and T2 is equivalent to a NPN transistor.

The quasi-two-way IO principle has been said, the only difference between open-leak input and quasi-two-way IO is that the open-leak input loses the external pull-up resistor. Open-drain input if you want to input high-voltage normal, T2 off, IO level to rely on the internal pull-up resistance to pull into a high level, if there is no internal pull-up resistor IO level is an unsteady state. Specification 51 single-chip microcomputer P0 port acquiescence is open and leaky input, if to use the time division internal demand plus pull resistance. And strong push-pull input is a relatively strong driving ability, such as figure 9-1 in the third small picture, when the external input of a high current is normal, through the MOS tube direct input current, no resistance current limit, the current input ability is also comparable; if the external input is a low level, then the reverse current can also be very large, a feature of strong push-pull is the drive ability.

Single-chip microcomputer IO also has a form called high resistance state. Usually we use as output pins, we can set the IO port to high resistance state, high resistance state lead drama itself if suspended, the time measured by the multimeter can be high or low, its shape completely depends on the level of the internal output signal, the equivalent resistance of the high resistance state pin to GND is very large (in fact, it is equivalent to infinite, but in practice it is always infinite rather than infinite), so it is called high resistance.

These are the four forms of the IO port of the single-chip microcomputer, in our 51 single-chip microcomputer learning process, the secondary use is quasi-two-way IO port, with the deepening of our study, other forms will also have contact, here introduced to everyone for further study.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.