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If your computer does not have an RS-232 serial port, low cost USB-to-RS-232 serial cables are available; contact Mosaic Industries for details. If your computer does not have an RS232 serial port, low cost USB-to-RS232 serial cables are available; contact Mosaic Industries for details. The PDQ Single Board Computer (SBC) has two asynchronous serial communications ports named Serial1 and Serial2. If you ever wanted to connect to device in the same building (e.g. to machinery on production hal) and to you have to go to it to connect your computer. The Serial1 and Serial2 ports have identical communications capabilities, although more of the Serial1 signals (both RS232 and RS485) are made available on the Docking Panels headers and connectors. These protocols are summarized on this page, but for more information regarding their data formats and their use for simplex or multi-drop serial lines, consult Understanding Serial Communications (but keep in mind that that page is directed to the use of the UART Wildcard, so it uses different driver functions). Each RS232 driver uses inverting logic and implements a single-ended bipolar output voltage (that is, one signal that swings above and below ground). RS232 uses inverse logic; that is, a positive bit at the HCS12 UART is inverted by the onboard RS232 driver chip and appears as a negative signal on the serial cable.

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 RS232 driver and receiver use separate conductors on the serial cables, enabling full duplex communications. Similarly, when establishing the transmit mode, the application software is responsible for ensuring that the RS485 receiver is not disabled until all expected characters have been received. The RS422 driver and receiver use separate differential conductor pairs on the serial cables, enabling full duplex communications. Characters may be lost if the transmit driver is turned off while pending characters are still being transmitted. Customary product on your driver boasts a built-in bi-color Motivated warning which gives the best neighborhood diagnostic make it easy for via presenting to just about just about any change out of all of the set subject natural world and aside from that delivering the visibility of any sort of heater management.

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. Because differential signals have inherently better signal-to-noise properties, reliable RS422 communications can be sent over much longer distances compared to RS232. RS485 is a half duplex version of RS422 that is capable of multi-drop operation. Newer protocols include the full duplex RS422 and the half duplex RS485 protocols, each of which drives differential 0 to 5 volt signals on the serial cable. Note that the local and the remote must share a common ground, so a minimum of 3 wires are required for half duplex RS485 communications: a pair of transceive wires and a common ground. RS232 is by far the most common serial protocol, and is the default protocol for both of the PDQ Board’s serial ports. Because a single pair of conductors is used for both transmission and reception, RS485 is useful for multi-drop applications in which a master communicates with multiple slave serial devices, or nodes. The master and slave could even exchange ascii QED-Forth commands. The master and slave could even exchange ascii QED-Forth operating system commands. Having a second serial port is also handy for system debugging.

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. RS485 uses the same differential signaling scheme as RS422, and hence has the same superior signal-to-noise characteristics and range described above. Each of the two channels on the UART Wildcard can be configured for RS232, RS422, or RS485. In the simplest scheme, all RS485 transceivers come up in receive mode when the interface is initialized, and each transceiver node has a unique address known to it and the master. Care must be taken when changing an RS485 node from transmit mode to receive mode, or visa versa. They should generally not be needed, except if you use long cables, multiple RS485 devices, and resistive termination. The termination also includes pull up and pull down resistors to establish fail-safe bias for each data wire for the case when the lines are not being driven by any device. Without termination resistors, signal reflections off the unterminated end of the cable can cause data corruption. Regardless of the network, however, there are only four signals used: SCK provides a synchronized clock, MOSI and MISO signals are used for data transmission and reception, and /SS configures the QScreen as a master or slave device.

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