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The driver must output between 5V and 15V in magnitude into a load of 3kΩ to 7kΩ. The driver must not be able to output more than 100mA when shorted to any other conductor in the cable, must not be able to output more than 25V and must be able to handle an open circuit, or a short to any other conductor in the cable. The local and remote must share a common ground, so all serial cables include at least one ground conductor. The words port and channel are used interchangeably to refer to a serial communications link. Is port re-entrant. - State driven Xmodem and Ymodem on multiple ports simultaneously. RS-232 defines thirteen "standard" interface types lettered A through M. None of these match IBM's implementation of its serial port. PURPOSE AND SCOPE OF COVERAGE - This standard is applicable to the interconnection of data terminal equipment (DTE) and data circuit-terminating equipment (DCE) employing serial binary data interchange. RS-485 discusses that it is used for devices up to 10Mbit/S, then says they need not be limited to 10Mbps. It also states that "the upper bound is beyond the scope of this Standard".

This limited the open circuit voltage to ±12V. Each RS232 driver uses inverting logic and implements a single-ended bipolar output voltage (that is, one signal that swings above and below ground). Most modems communicate using RS232 and a set of hardware handshaking signals used to regulate data flow. See the instructions on the converter you are using. See the section on grounding for a discussion of this "extra wire". To add a little extra noise margin, use 680 Ω resistors and you have one of the more common biasing networks used on a RS-485 network. Should also be used on RS-485 networks if the driver is always enabled. Another problem with this scheme is that the transmitter needs to stay enabled during the transmission of all of the data. Serial data is shifted out least-significant-bit first. The serial output at the UART idles at the logic high (mark) level. One to two logic-high stop bits mark the end of a character.

RS-422 specifies the electrical levels of one transmitter to one of more receivers on a single pair of wires. Each RS422 driver transmits a differential pair of output signals at 0 and 5 volts. In fact, a single driver chip on the UART Wildcard is used to implement both RS422 and RS485 communications for a given serial channel. The primary difference between RS-422 and RS-485 is that RS-485 requires two wires in a single pair which all devices transmitters and receivers are connected to, and RS-422 typically uses two or more pair in which only one transmitter and up to ten receivers are connected to a single pair. These examples are for a single 120 Ω termination. If you run a data rate of less than 30kBit and don't need long cables, the termination resistors are probably not required. The serial interface is asynchronous, meaning that there is no clock transmitted along with the data. A break sequence forces the serial output to a logic low (space) at the UART. At the UART, a logic high (5 volts) is called a mark, and a logic low (0 volts) is called a space. The RS422 receiver converts the differential signal to the 0 to 5 volt logic signal required by the UART circuitry.

Newer protocols include the full duplex RS422 and the half duplex RS485 protocols, RS485 standard each of which drives differential 0 to 5 volt signals on the serial cable. The RS232 driver and receiver use separate conductors on the serial cables, enabling full duplex communications. The UART Wildcard implements these optional RS232 modem handshaking signals on channel 1. The handshaking signals can be disabled and/or ignored by applications that do not need them. Owing to hardware constraints, if modem handshaking is needed on UART channel 1, then channel 1 must be configured for RS232, and channel 2 cannot be configured for RS232 communications. Each of the two channels on the UART Wildcard can be configured for RS232, RS422, or RS485. Multiple channels allow the DIRTX8 to transmit individual codes out on each channel, which eliminates problems where different Hi-Fi components share the same code. Each of the two channels on the UART Wildcard implements two 16-character FIFOs, one for outgoing characters and one for incoming characters.