Robotics/Computer Control/The Interface/Networks

Sometimes a single controller isn't sufficient to control your robot. Then you'll be needing a way to connect all those controllers, preferably without sacrificing too many pins or expensive ICs. Of course this problem has been solved a long time ago and there are quite a number of different standards each having their own advantages and disadvantages. Standards There are many different standards on connecting 2 or more µcontrollers (or computers), but here are the most used standards: (See Serial communications bookshelf for more detailed information about serial communication standards) I²C Inter-Integrated-Circuit-bus or Two-wire serial bus: Used to connect ICs on a single board. The bus has one clock and one data line. Both the clock and data line are pulled high and device only drives the lines low. There are plenty of ICs available with build-in I²C interface including many of the modern µcontrollers. µcontrollers with build in I²C support: ATMEGA8 ATMEGA16 ATMEGA32 ATMEGA64 ATMEGA128 ATMEGA8535 Some I²C ICs: MAX5380/5381/5382: 8Bit DAC PCF8574: 8bit I/O-expander for I²C-bus LM75: digital temperature sensor The I²C protocol can also be performed in software and is usually referred to as bit-banged I²C. See:Philips Semiconductors RS232 Recommended Standard 232: Better known as the serial port on a PC. Used to connect two devices. See: Further down the page RS422 Recommended Standard 422: industrial version of RS232. Much better than RS-232 at resisting interference. See: RS422 tutorial RS485 Recommended Standard 485: Better version of RS422: allows more than 2 devices to be connected together. (usually up to 32 devices) RS232 <-> RS485 converters: LTC485CN8: DIL8 SN75LBC176D: SOIC8 See: RS485 tutorial CAN Acronym stands for "Controller Area Network." More complicated network. Used in automotive and domotica. Originally developed by Bosch in Germany. Limited to 1 Mbps in theory; with required overhead, protocol is slower than 1 Mbps. Data is delivered in packets of 8 bytes. CAN is frequently referred to as CANbus. See: Philips Semiconductors 1wire This bus uses 1 wire to supply power and communication to a IC. Used for temperature sensors and other low-power ICs. Despite the name, a second wire, ground, is used to complete the circuit. Data is sent to the IC by switching the wire between high and low. A built-in capacitor provides the IC with power during the low parts of the signal. This bus is intended for low-power devices, like temperature sensors. See: Maxim-IC SPI SPI(Serial peripheral interface) is a 4-wire full duplex bus. The bus has a clock, transmit, receive, and select line. One device controls communication on the bus. When connecting multiple devices, each device is connected to the master with a separate select line and the master selects only one device at a time. Further reading Embedded Systems/Common Protocols Serial Programming