Single master systems (many other communications schemes are available) offer a straight forward and simple means of avoiding "data collisions" in a typical 2-wire, half-duplex, multi-drop system. Systems of this type (4-wire, rs485 cable half-duplex) are often constructed to avoid "data collision" (bus contention) problems on a multi-drop network (more about solving this problem on a two-wire network in a moment). RS-485 signals are used in a wide range of computer and automation systems. RS-485 and RS-422 can interoperate with certain restrictions. In a finished instrument, either or both channels can be used to communicate with other serial devices, or with other computers and/or terminals using RS232 or rs485 cable. RS232’s greatest benefit is its universality; practically all personal computers can use this protocol to send and receive serial data. The secondary channel is very useful for debugging application programs that communicate with other computers or I/O via the primary channel. Having a second serial port is also handy for system debugging. Since both channels can operate simultaneously and independently, serial debugging can be performed while the application program is communicating via its primary channel.

In other words, each local UART on the wildcard can both send data to and receive data from a remote UART on the other end of a connecting serial cable. Care must be taken that an SC connection, especially over long cable runs, does not result in an attempt to connect disparate grounds together - it is wise to add some current limiting to the SC connection. Standards have been developed to insure compatibility between units provided by different manufacturers, and to allow for reasonable success in transferring data over specified distances and/or data rates. In its simplest form, a pair of converters from RS232 to RS422 (and back again) can be used to form an "RS232 extension cord." Data rates of up to 100K bits / second and distances up to 4000 Ft. A true multi-point network consists of multiple drivers and receivers connected on a single bus, where any node can transmit or receive data. In that case you may terminate the lines with a series RC network comprising a 0.1 μF capacitor in series with a 120 Ω resistor.

Any of these conditions may generate an interrupt if the SPIE (SPI interrupt enable) bit in the SPCR control register is set. It may be that only the byte sent from the master to the slave is meaningful; nevertheless, each device simultaneously transmits and receives one byte. The distinction between master and slave is an important one. When the /SS input goes low, the slave (or QScreen in this case) transfers data in response to the SCK clock input that is initiated by the master. Even though the MOSI pin is not connected to anything, the master initiates a transmission using a "dummy" byte. The hardware detects the start-bit of the transmission and automatically enables (on the fly) the RS485 transmitter. Once a character is sent the hardware reverts back into a receive mode in about 1-2 microseconds (at least with R.E. Any number of characters can be sent, and the transmitter will automatically re-trigger with each new character (or in many cases a "bit-oriented" timing scheme is used in conjunction with network biasing for fully automatic operation, including any Baud rate and/or any communications specification, eg. With the introduction of "automatic" repeaters and high-impedance drivers / receivers this "limitation" can be extended to hundreds (or even thousands) of nodes on a network.

Differential signals can help nullify the effects of ground shifts and induced noise signals that can appear as common mode voltages on a network. RS422 (differential) was designed for greater distances and higher Baud rates than RS232. When communicating at high data rates, or over long distances in real world environments, single-ended methods are often inadequate. The specification allows for data transmission from one transmitter to one receiver at relatively slow data rates (up to 20K bits/second) and short distances (up to 50Ft. @ the maximum data rate). The connection between two or more elements (drivers and receivers) should be considered a transmission line if the rise and/or fall time is less than half the time for the signal to travel from the transmitter to the receiver. Differential data transmission (balanced differential signal) offers superior performance in most applications. Electronic data communications between elements will generally fall into two broad categories: single-ended and differential.