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. A ground connection is also necessary to ensure that the communicating devices have a common voltage reference. It is important to note that when the CPHA bit is 0, the /SS line must be de-asserted and re-asserted between each successive data byte exchange (68HC11 Reference Manual, Section 8.3.2). If the CPHA bit is 1, rs485 cable the /SS line may be tied low between successive transfers. A modem (modulator/demodulator) provides a way of encoding digital data as a set of audio signals that can be sent over a telephone line. RS423 is another single ended specification with enhanced operation over RS232; however, it has not been widely used in the industry. RS422 devices. These networks are often used in a half-duplex mode, where a single master in a system sends a command to one of several "slave" devices on a network.

Two RS485 transceivers are present on the PDQ Board, one for each channel. If your computer does not have an RS232 serial port, low cost USB-to-RS232 serial cables are available; contact Mosaic Industries for details. A break sequence forces the serial output to a logic low (space) at the UART. For an off, mark or logic 1 state, the driver's A terminal is negative relative to the B terminal. One to two logic-high stop bits mark the end of a character. So, for eight data bits with a parity bit, M would be set (equal to one) in order to add an extra bit to each byte transmitted, and PE would be set in order to make that extra bit be used as a parity bit. Systems of this type (4-wire, 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). To solve the "data collision" problem often present in multi-drop networks hardware units (converters, repeaters, micro-processor controls) can be constructed to remain in a receive mode until they are ready to transmit data. DH 485 is a proprietary communications protocol used by Allen-Bradley in their line of industrial control units.

Modem to phone line communications use rates of 110, 150, 300, 600, 1200, 2400, 3000, and 3200 baud. Each serial port can be configured for the RS232 or RS485 protocol, and runs at standard baud rates up to 115,200 bits per second. The Serial 1 and Serial2 ports can be configured for either RS-232 or RS-485 communications at standard baud rates up to 115200 bits per second. RS-485 serves as a physical layer for the AES3 digital audio interconnect. RS-485 does not specify any connector or pinout. To ensure that no two devices drive the network at the same time, it is necessary that each slave device be able to disable it’s own RS-485 data transmitter. Just like it’s older brother RS232, RS485 is a form of serial communication. 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 2-wire synchronous IIC (Inter-IC) bus provides multi-drop signaling at rates up to 100 Kbaud.

RS422 (differential) was designed for greater distances and higher Baud rates than RS232. Differential data transmission (balanced differential signal) offers superior performance in most applications. Differential signals can help nullify the effects of ground shifts and induced noise signals that can appear as common mode voltages on a network. RS485 extends the common mode range for both drivers and receivers in the "tri-state" mode and with power off. RS485 meets the requirements for a truly multi-point communications network, and the standard specifies up to 32 drivers and 32 receivers on a single (2-wire) bus. A true multi-point network consists of multiple drivers and receivers connected on a single bus, where any node can transmit or receive data. 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. All of the serial ports are supported by pre-coded C-language software drivers that make it easy to exchange data. The protocols are described in turn.