Computer I/O (input/output) port allow the CPU to control devices in the outside world.Signals may be output to control lights,motors and heaters for example. Conversely,signal from the outside world,provided by sensors such as simple switch,thermistors,opto diodes (light sensors) and pressure sensitive devices, may be input to the CPU.These signals can be analyzed and processed, with the CPU outputting new signal in consequence.So like sea ports along the coast which allow goods to be brought into and out of a country,I/O port allow signals to pass into and out of a computer.
The word 'signal' in this context is meant to imply an electrical or electronic value,or variation in value,which carries information.Signals have no power they only carry information.You can't simply connect devices to the ports and expect them to work.Obviously (at least I hope it's obvious) you can't connect ordinary,mains light bulbs to output ports .A 60W main lamp needs 240V at 250mA ; the output ports of 6502 and Z80 systems can only manage a maximum voltage of 5V, at a current some hundred times less than the 250mA quoted for the lamp.The signals could not even light up a small LED but they can be amplified of course.
The television signals appearing at the end oh the aerial cable are of the order of microvolt and they can't drive anything either.But all the complex information about the sound,vision and color,together with synchronizing
pulses and teletext,are carried in the signal.It has only to be processed and amplified by the television receiver.
Turning the low voltage,low current computer signals into something which can drive light,motors or heaters requires 'interfacing'.The interface is an electronic block which accept low level signals,and condition them so that they are suitable in amplitude(both voltage and current)for driving the peripheral to which the interface is connected.
The word 'signal' in this context is meant to imply an electrical or electronic value,or variation in value,which carries information.Signals have no power they only carry information.You can't simply connect devices to the ports and expect them to work.Obviously (at least I hope it's obvious) you can't connect ordinary,mains light bulbs to output ports .A 60W main lamp needs 240V at 250mA ; the output ports of 6502 and Z80 systems can only manage a maximum voltage of 5V, at a current some hundred times less than the 250mA quoted for the lamp.The signals could not even light up a small LED but they can be amplified of course.
The television signals appearing at the end oh the aerial cable are of the order of microvolt and they can't drive anything either.But all the complex information about the sound,vision and color,together with synchronizing
pulses and teletext,are carried in the signal.It has only to be processed and amplified by the television receiver.
Turning the low voltage,low current computer signals into something which can drive light,motors or heaters requires 'interfacing'.The interface is an electronic block which accept low level signals,and condition them so that they are suitable in amplitude(both voltage and current)for driving the peripheral to which the interface is connected.
