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The RS232 protocol specifies the use of two separate grounds, a signal ground and a protective (or "chassis") ground. RS232’s greatest benefit is its universality; practically all personal computers can use this protocol to send and receive serial data. The pinout of the QScreen’s Serial Header (H5), QScreen’s Field Header (H3), and the Serial Connectors are shown in the following tables. You can enter the data relating to the MQTT Broker you want to use; the name of the Topic to be used to control it and to read the periodic transmissions of the humidity percentage is shown. The probe is available with 0.8m or 3m cable; and possibly can be replaced by anyone with good dexterity. We can gain insight into the operation of the RS232 protocol by examining the signal connections used for the primary serial port in Table 9 6. The transmit and receive data signals carry the messages being communicated between the QScreen Controller and the PC or terminal. A jumper, J3, configures the primary serial port for either RS232 or RS485 operation. The hardware detects the start-bit of the transmission and automatically enables (on the fly) the RS485 transmitter. The only difference between the master and slave devices is that the master initiates the transmission.

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. Any number of characters can be sent, and the transmitter will automatically re-trigger with each new character (or in many cases a "bit-oriented" timing scheme is used in conjunction with network biasing for fully automatic operation, including any Baud rate and/or any communications specification, eg. Each UART (sometimes referred to as a "USART") controls the serial-to-parallel and parallel-to-serial conversion and performs all of the timing functions necessary for one asynchronous serial communications link. In this case, cable connections must be made to Serial 1 at pins 5 and 6 of the 10-pin Serial Header or pins 7 and 8 on the 24-pin Field Header. In this case, cable connections may be made to Serial 1 on either the 10-pin Serial Communications Header or the Serial 1 Connector. Depends what you mean by a serial cable - Fibre, Ethernet, RS232, RS485, RS422, USB, HDMI, SMPTE292 are all examples of serial communications media. It can be used for multi-point and point-to-point communications applications. It is NOT necessary to introduce long delays in a network to avoid "data collisions." Because delays are NOT required, networks can be constructed, that will utilize the data communications bandwidth with up to 100% through put.

While a multi-drop "type" application has many desirable advantages, RS422 devices cannot be used to construct a truly multi-point network. A true multi-point network consists of multiple drivers and receivers connected on a single bus, where any node can transmit or receive data. Typically one device (node) is addressed by the host computer and a response is received from that device. To avoid contention on the RS485 bus, rs485 cable the application software must assure that only one transmitter is enabled at a time. Because the software UART is interrupt based, competing interrupts that prevent timely servicing of the Serial2 interrupts can cause communications errors on the secondary serial channel. 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 serial communications cable is also supplied with QScreen Starter Kits. The default serial routines used by the onboard kernel assume that full duplex communications are available, so you cannot use the RS485 protocol to program the controller.

Because all of the serial I/O routines on the PDQ Board are revectorable, it is very easy to change the serial port in use without modifying any high level code. If you do this now, remember to move the QScreen Controller’s serial connector back to Serial Port 1, and to change the terminal’s baud rate back to 19200 baud using the "Comm" item under the terminal’s "Settings" menu. 1200 is the baud rate that you choose; you can specify any standard baud rate up to 4800 baud. TXsoil is a compact and low consumption sensor that can measure and transmit the humidity of the ground WiFi or RF or GSM. Chassis and signal grounds are connected together to the digital ground (GND) signal. To provide a convenient means of attaching two grounds to the serial cable, there are several pins (labeled GND) on the communications connector that are connected to the controller’s ground plane.