双向IO口(国外英文资料).doc

双向IO口(国外英文资料) The quasi-bi-directional method can only be used for the digital input and output, the input is weak and the port is only two states: high or low. 2: both sides can be used to simulate input output except for digital input and output, and the port is set to high resistance input when the input time is set. A two-way port has three states: high, low, or high resistance. 3: the initial state and quasi two-way reset condition for 1 mouth, two-way mouth as the high impedance state. With some of the comparator of single chip microcomputer, the input end of the comparator can only do in a double mouth, cant do in quasi double mouth. So the first step in the software design is the set of I/O port. Standard of 51 kernel single-chip computer IO mouth, P0 mouth is bi-directional tri-state I/o port, P1, P2, P3 is quasi two-way IO mouth, no direction control, when doing the input needed to write 1 port data register first (can also be used as for the output at this time, the port output high level). Control of the single chip microcomputer, is actually the control of I/O port, regardless of what kind of control microcontroller was carried out on the outside, or accept external control, are conducted through the I/O port. There are a total of P0, P1, P2, P3, and P3, 4 8-bit input/output ports, each with a latch, output driver, and input buffer. The four I/O ports can be used as input and output, where P0 and P2 are commonly used for access to external storage. The series 51 single-chip machines have four I/O ports, each of which is eight quasi-bidirectional ports, with a total of 32 pins. Each port includes a latch (that is, special registers P0 ~ P3), an output driver, and an input buffer. The four ports are generally represented as P0 ~ P3. Each of these four ports can be used as a quasi-bi-directional universal I/O port in a system with no external extended memory. In a system with an extended memory, the P2 port is a high 8 address line, and P0 is a low 8-bit