Each specific IO device can be connected to others using specific interfaces, for instance, an IO device connects and is interfaced to an LCD controller, keyboard controller, or print controller using specific interface. Bus communication simplifies the number of connections and provides a common protocol for interconnecting different or same type of IO devices.
Any device that is compatible with a system’s IO device can be added to the system, provided that a suitable device driver program is available, and a device that is compatible with a particular IO bus can be integrated into any system that uses that type of bus. This makes the systems that use IO buses very flexible, in contrast to direct interconnections between the processor and each IO device, also, it allows system support to many different IO devices (depending on the needs of its users), and allows users to change the IO devices that are attached to the system as their requirements change.
The main shortcoming of an IO bus (and any other bus in general) is that each bus has a fixed bandwidth that must be shared by all the devices, which connect to the bus. Additionally, electrical constraints i.e. wire length and transmission line effects cause buses to have less bandwidth than using the same number of wires to connect just two devices.
IO devices communicate with the processor through an IO bus, which is separate from the memory bus that the processor uses to communicate with the memory system. Embedded systems connected internally on the same IC or systems at very short and long distances can be networked using the following types of IO buses, each operating according to specific protocols.
- Using a serial IO bus allows a computer or controller or embedded system to interface and network with a wide range of IO devices without having to implement a specific interface for each IO device. When the IO devices in the distributed embedded systems are networked at long distances of 25 cm and above, all can communicate through a common serial bus.
- Using the internet or intranet, a computer, controller or embedded system’s IO device can interface globally and can network with other systems or computers and a wide range of devices in the distributed systems.
- Using parallel IO bus allows a computer or controller or embedded system to interface with a number of internal systems at very short distances without having to implement a specific interface for each IO device.
- Using a wireless protocol permits a handheld computer, controller, or embedded system IO device to interface and network with a number of handheld system IO devices at short distances of up to 100 m using a wireless personal area network (WPAN) protocol, without having to implement a specific wireless interface for each IO device.
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