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The ports are points where input signals are applied or output signals taken. Its behavior is completely specified by a matrix of parameters relating the voltage and current at its ports, so the internal makeup or design of the circuit need not be considered, or even known, in determining the circuit's response to applied signals.
The term can also be used as part of an action; to "perform I/O" is to perform an input or output operation. I/O devices are the pieces of hardware used by a human (or other system) to communicate with a computer. For instance, a keyboard or computer mouse is an input device for a computer, while monitors and printers are output devices.
Input and output voltages are usually, but not always, limited to the supply voltage of the device with the GPIOs, and may be damaged by greater voltages. A GPIO pin's state may be exposed to the software developer through one of a number of different interfaces, such as a memory-mapped I/O peripheral, or through dedicated IO port instructions.
Figure 1: Example two-port network with symbol definitions. Notice the port condition is satisfied: the same current flows into each port as leaves that port.. In electronics, a two-port network (a kind of four-terminal network or quadripole) is an electrical network (i.e. a circuit) or device with two pairs of terminals to connect to external circuits.
Memory-mapped I/O is preferred in IA-32 and x86-64 based architectures because the instructions that perform port-based I/O are limited to one register: EAX, AX, and AL are the only registers that data can be moved into or out of, and either a byte-sized immediate value in the instruction or a value in register DX determines which port is the source or destination port of the transfer.
Input/output integrated circuits (28 P) P. Punched card (2 C, 16 P) T. ... Input method; Input/output completion port; Instrument driver; Iometer; J. Jog dial; K. KVM ...
Later single-chip microcontrollers have input and output pins available. These input/output circuits usually do not provide enough current to directly operate devices like lamps or motors, so solid-state relays are operated by the microcontroller digital outputs, and inputs are isolated by signal conditioning level-shifting and protection circuits.
The switch circuit creates a continuous metallic path for current to flow (in either direction) between its input and its output. The semiconductor logic gate, on the other hand, acts as a high- gain voltage amplifier , which sinks a tiny current at its input and produces a low-impedance voltage at its output.