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Serial communications computer boards are modular boards that add serial ports to a computer system.
Understanding Serial Boards
Serial and parallel communications are two methods of sending data between two microprocessors or computer devices. Parallel communication involves sending data all at once using multiple channels (wire conductors, optical fibers, etc.). While parallel data transfer is capable of transmitting large amounts of data very quickly, its need for multiple channels requires more space and resources, and may result in crosstalk interference between channels.
Serial (left) and parallel communications.
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Serial systems tend to be smaller and cheaper to produce when used in large-scale networks because they only require one channel. Serial technology is also beginning to supersede parallel in smaller networks due to technological improvements in signal integrity and transmission speed.
Serial boards plug into a computer bus in order to expand the system's number of serial ports. These products do not typically include an enclosure and are designed to mount inside a computer.
For information about a board's serial protocol options, please visit GlobalSpec's Serial Adapters Selection Guide. Serial communications boards may feature one or many serial ports operating at various data transfer rates.
Network / Bus
When creating a serial network, all of the devices must communicate using an agreed-upon format, many of which are described below. In terms of serial boards, the network type refers to the type of bus with which the card connects.
Ethernet cables transmit data in packets called frames, each of which contains the source address, the destination address, and error-checking functionality. Ethernet is standardized in IEEE 802.3, which describes the media access control (MAC) of both the physical layer and the data link layer.
10Base-T is a 10-Mbps standard implemented on a twisted-pair cable with modular connectors. It uses pins 1 and 2, 3 and 6, in an 8 position modular plug / jack, typically an RJ-45. Patch cables for 10Base-T Ethernet are usually pinned to the EIA / TIA 568A or 568B standard. 10Base-T is the most popular type of Ethernet.
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Universal serial bus (USB) is used to connect personal computers (PCs) and peripherals such as mice, keyboards, printers, digital cameras, and mass storage devices. USB cables are also used in factory environments, sometimes with a locking mechanism, for connecting USB industrial I/O devices to computers.
The USB specification was designed for desktop environments and limits the length of cables to 5 meters (m) between full-speed devices and 3 m between low-speed devices.
PC cards adhere to standards set by the Personal Computer Memory Card International Association (PCMCIA). All PC cards have the same width and length dimensions but vary in thickness. PCMIA cards use a 68-pin host socket, while PC/104 cards use a 104-pin socket.
A PC card and slot on a laptop. Image credit: Boards.ie
Peripheral component interconnect (PCI) is a local bus system capable of 32 or 64 bit transfer rates at a clock speed of 33 MHz. CompactPCI buses use the same electrical standard as the PCI bus and is packaged as a Eurocard. cPCI buses are used extensively in applications requiring high-speed data transfer.
Controller area network (CAN) bus is a standard which allows communication between controllers and/or host computers. CAN bus is frequently used in automotive and other applications with harsh conditions. It allows operational data rates of up to 1 Mbps and provides excellent error detection and confinement capabilities.
An automotive CAN bus network. Image credit: canbuskit.com
The process field bus (PROFIBUS®) is popularly used in factory automation, process automation, motion control, and other industrial uses. This standard is suitable for both fast, time-critical applications and complex communication tasks. PROFIBUS is a registered trademark of PROFIBUS International.