1 running at the prior established baud rate (typically 19200 baud). The default baud rate after a factory cleanup is 115200 baud. 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. The PDQ Single Board Computer (SBC) has two asynchronous serial communications ports named Serial1 and Serial2. The PDQ Board’s transmit data signal /TxD1 (pin 2 on the 9-pin serial connector) is connected to the terminal’s receive data signal /RxD (pin 2 on its 9-pin connector). Rather, it relies on software handshaking via transmission of XON/XOFF characters (ascii 0x11 and 0x13, respectively) to coordinate data transfer and ensure that information is not lost when one of the communicating parties is busy. See page 7 of the Laurel digital panel meter manual, page 7 of the Laurel counter manual, page 8 of the Laurel scale meter manual, or page 8 of the Custom ASCII protocol manual. We can gain insight into the operation of the RS232 protocol by examining the signal connections used for the primary serial port in the above table. The RS232-RS485 adapter circuit diagram is show below, RS232 DB9 is used as the RS232 port, while only a terminal block is used as RS485 connector.

The following table shows the connection diagram for a standard 9-pin serial cable. The following table summarizes the available serial channels. The pinout of the PDQ Board’s Communications Header (H2), Docking Panel’s Communications Header (H1), and the Docking Panel’s Communications DB-9 Connectors are shown in the following tables. The primary and secondary serial communications ports are accessible through the PDQ Board's 10 pin, dual row Communications Header (H2) and through the Docking Panel's 10 pin, right-angle, dual row Communications Header (H1) and individual DB-9 Serial 1 and Serial 2 connectors. Two asynchronous communications ports named Serial1 and Serial2 can each be configured for RS232 or RS485 protocols. 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. RS232 is by far the most common serial protocol, and is the default protocol for both of the PDQ Board’s serial ports. PCs are normally not equipped with an RJ11 socket for serial RS232 communications.

Using the primary serial port is easy. If your PC or controller only has RS232 port then you need an RS232 to RS485 converter or adapter for your PC or controller. Although the RS232 protocol specifies functions for as many as 25 pins, each communications channel requires only three for simple serial interfaces: /TxD1 (transmit data), /RxD1 (receive data), and DGND (digital ground). The RS485 data direction of Serial1 and Serial2 are controlled by the PJ0 and PJ1 processor pins, respectively. 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. If your computer does not have an RS232 serial port, low cost USB-to-RS232 serial cables are available; contact Mosaic Industries for details. Please contact Mosaic Industries if you need this custom configuration. RS232’s greatest benefit is its universality; most personal computers can use this protocol to send and receive serial data. You can use it to communicate with other devices. It can transfer as well as process the data. For this reason, frame-level cyclic redundancy checks are much more widely used for validating data from serial links, network connections and storage media.

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). Many terminals and PCs, however, do rely on hardware handshaking to determine when the other party (in this case the PDQ Board) is ready to accept data. RS485 is another protocol supported by the primary serial port on the PDQ Board. Even RS485 is not commonly as popular as RS232 it is extremely useful for converters in industrial and commercial environments. Most computers conform to IBM PC AT-compatible RS232 interfaces which use 9-pin D-Type connectors, consequently the PDQ Board brings out its serial ports to two female 9-pin D-Type connectors on the Docking Panel. These 9-pin standard DB-9 serial connectors are located on the back of the Docking Panel.

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