Question

what is the difference between a port and a signal?  

Answer 1

we can define both port and signal in various respects of system...

port:-

(1).In computer and telecommunication devices:-Port is generally a specific place for being physically connected to some other device, usually with a socket and plug of some kind. Typically, a personal computer is provided with one or more serialports and usually one parallel port. The serial port supports sequential, one bit-at-a-time transmission to peripheral devices such as scanners and the parallel port supports multiple-bit-at-a-time transmission to devices such as printers.

(2).In programming:-port is a "logical connection place" and specifically, using the Internet's protocol, TCP/IP, the way a client program specifies a particular server program on a computer in a network. Higher-level applications that use TCP/IP such as the Web protocol, Hypertext Transfer Protocol, have ports with preassigned numbers. These are known as "well-known ports" that have been assigned by the Internet Assigned Numbers Authority (IANA). Other application processes are given port numbers dynamically for each connection. When a service (server program) initially is started, it is said to bind to its designated port number. As any client program wants to use that server, it also must request to bind to the designated port number.

(3).In VHDL:-

Ports are a part of the block interface: external - if defined by a design entity, or internal - if defined by a block statement. Each element listed in a port interface list declares a formal port, which provides a channel for dynamic communication between a block and its environment.

In practice,ports are most often used in entities and components, where they serve for declaring interface signals of a design entity (system design) or component, respectively

signal:-

(1).In electronics:-A signal is an electric current or electromagnetic field used to convey data from one place to another. The simplest form of signal is a direct current (DC) that is switched on and off; this is the principle by which the early telegraph worked. More complex signals consist of an alternating-current (AC) or electromagnetic carrier that contains one or more data streams.

(2).In telephony:- In telephony, a signal is special data that is used to set up or control communication.

(3). In VHDL:-Signals are the primary objects describing a hardware system and are equivalent to "wires". They represent communication channels among concurrent statements of system's specification. Signals and associated mechanisms of VHDL (like signal assignment statements, resolution function, delays, etc.) are used to model inherent hardware features such as concurrency, inertial character of signal propagation, buses with multiple driving sources, etc. Each signal has a history of values and may have multiple drivers, each of which has a current value and projected future values. All signal parameters are accessible by means of signal attributes.