The RS232 protocol specifies the use of two separate grounds, a signal ground and a protective (or chassis) ground. Chassis and signal grounds are connected together to the digital ground (DGND) signal. Two devices are at the ends of the cable, while others are connected somewhere in between. Although the devices would share the same network, communications would only be understandable by members of the same group. 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). 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). A jumper labeled "1 485En" (J4) enables RS485 operation on the Serial1 port if the jumper cap is installed, and configures Serial1 for RS232 operation if the jumper cap is not installed.

The SPIE bit in the SPCR (SPI control register) enables SPI interrupt handling. The clock’s polarity is controlled by a bit named CPOL (clock polarity) and its phase is controlled by CPHA (clock phase). If A is negative with respect to B, the state is binary 1. The reversed polarity (A positive with respect to B) is binary 0. The standard does not assign any logic function to the two states. 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. If PT is set, all transmitted bytes with a parity bit will have an odd number of total '1' bits. When PE is cleared (equal to zero), the most-significant bit of each transmitted character will be a data bit. All of the RS232 signals start with the / (slash, pronounced not) character to indicate that the signals on the serial cable are logically inverted. Laureate meter and LT series transmitters support the Modbus RTU protocol and Laurel’s simpler ASCII character based Custom ASCII protocol.

If multiple analog input meters or transmitters are digitally addressed in command mode on an RS485 line using the Modbus RTU protocol or the Custom ASCII protocol, the rate becomes about 2 readings per second. Thus in the table, /RTS1 is connected to /CTS1, and /DSR1 is connected to /DTR1 and /DCD1 onboard the PDQ Board using zero ohm shorting resistors. By default, the RS485 connections are not brought out to the Docking Panel’s DB-9 Serial1 Connector, although custom placement of zero-ohm surface-mount resistors on the Docking Panel can route the RS485 signals to the DB-9. By default, the RS485 connections are not brought out to the Docking Panel’s DB-9 Serial1 Connector. 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. If your PC or controller only has RS232 port then you need an RS232 to RS485 converter or adapter for your PC or controller.

Contact Mosaic if you require RS485 signals to be routed to the DB-9 Connector. Please contact Mosaic Industries if you need this custom configuration. If your computer does not have an RS232 serial port, low cost USB-to-RS232 serial cables are available; contact Mosaic Industries for details. For Serial2 RS232 operation: Remove the jumper shunt from "2 485En" (J7). For Serial1 RS485 operation: Install the jumper shunt onto "1 485En" (J4). For Serial2 RS485 operation: Install the jumper shunt onto "2 485En" (J7). As described below, the RS485Transmit() function controls the RS485 data direction of each serial port. After a factory cleanup, Serial1 is the default serial port for program development and downloading. RS232 is by far the most common serial protocol, and is the default protocol for both of the PDQ Board’s serial ports. The default serial routines used to download programs to the operating system assume that full duplex communications are available, so you cannot use the RS485 protocol to program the controller.

If you adored this short article and you would like to obtain more info pertaining to rs485 cable kindly go to our own web-page.