Serial Communications
Each protocol builds on the older technology.
Physical | Signaling | Link | Comments |
RS232 | single end (signal+ground) | point to point | |
NMEA 0183 | Simple ASCII protocol for data transfer, most commonly used by GPS receivers. | ||
PPP | PPP allows connecting to a TCP/IP network over an RS232 connection, usually via modem and a telephone line. | ||
RS422 | differential | point to point | |
Localtalk | Networking for Apple computers | ||
RS485 | differential | bus, master slave (one controller many peripherals) | |
LonTalk | Networking for building control systems | ||
CAN bus | differential | bus, "Controller Area Network", widely used in automobiles. | |
USB | differential | "Universal Serial Bus", peripheral connections for computers; (one host controller, many peripherals) | |
NMEA 2000 | differential | Networking for maritime applications |
RS232 - point to point - one computer and one device per port. Defines a standard set of data rates but no software protocol. Can be half or full duplex.
NMEA 0183 - this is a simple software protocol that uses RS232 for its hardware layer. NMEA 0183 is used for exchanging information between a master station (usually a computer or a "chart plotter") and a controller or sensor. Originally NMEA 0183 was intended for use on boats but also widely used in GPS equipment, most GPS receivers can be progreammed to output a NMEA 0183 data stream.
RS422 - Like RS232 but with differential signaling. Still point to point.
RS485 - Differential signaling, nominally at 0-5V. Adds bus topology that can be half or full duplex. In half duplex mode there can be one master and many slave nodes. Master polls slaves to avoid contention; only one slave talks at a time. No software protocol defined.
CAN (Control Area Network) bus - devised by Intel and Bosch for automobiles. Uses collision detection, so any node can talk anytime it needs to.
USB Universal Serial Bus - now found on all new desktop computers and many peripherals; has pretty much replaced RS232 on computers. Like RS485, it uses half duplex and differential signaling. Like CAN, it has a software protocol defined. It also has connectors and cabling included in the specifications.
NMEA 2000 - complete specification for the physical and software communications; designed to be used on boats. NMEA 2000 is based on CAN, but like USB, the allowed data rate, connectors and cabling are included in the spec.