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The Silence() routine searches the incoming serial characters for a pre-determined keyword (for example, the ascii "name" of this particular slave). To use a QScreen as a slave in a multi-drop network, simply define a word, (named Silence(void), for example) that when executed calls RS485Receive() to wait for any pending character transmission to complete, then disable the transmitter, and then execute a routine such as Key() to listen to the communications on the serial bus. Setting the MSTR bit initializes the QScreen as a master, rs485 cable and clearing the MSTR bit initializes it as a slave. Setting SPE (SPI enable) to 1 turns on the SPI system. By setting this output LOW, the slave’s input /SS is pulled LOW. If you are using the QScreen as a master device, each external SPI device will require a separate select line (/SS). Only one active master may control the network at a time; however, the device that assumes the role of master may change according to an appropriate protocol.

Given a properly wired network and a properly configured SPCR control register, a master device may transmit a message by simply storing the byte to the SPDR data register. Capable of performing mathematical operations in the input channels, this high-speed reading and logging device utilized a 24-bit A/D converter enabling up to 1000 samples a second and a suite of connectivity options including a 10/100 Mbps Ethernet interface that allowed for access through a browser (HTTP), FTP (client and server), e-mail sending (SMTP), SNMP and Modbus TCP. Utilizing a series of dedicated interface devices, it allows PCs and industrial controllers to communicate. SPIE is a local interrupt mask that allows an interrupt to be recognized when an SPI data transfer has completed, or if a write collision or mode fault is detected. The symmetrical pin layout of the RJ11 sockets on the Unitronics PLCs allows an easy way of interconnecting the PLCs with both RS232 and RS485 communications. The InitSPI() function provides a convenient way to initialize the SPI as the master at a 2MHz baud rate.

The CPOL, CPHA, SR1 and SPR0 configure the SCK pin’s clock polarity, clock phase, and clock rate. The SPI can transfer data much more rapidly than an asynchronous serial link - its maximum rate is 2 Megabits/second. The QED-Forth kernel includes pre-coded drivers that configure and control the SPI for maximum speed data transfers. The /SS (active-low slave select) is typically used to enable data transfers by slave devices when it is active low. Although data byte transfers are easily executed once the network has been wired and configured properly, a carefully executed software protocol may be required to ensure data integrity. The received data byte is accessed by reading SPDR data register. If the /SS pin of the master is an input and if a low input level is detected, the processor sets the MODF bit in the SPI status register a "mode fault" condition. There are a variety of ways the MOSI, MISO, SCK and /SS pins on your QScreen Controller can be connected. For the QScreen, /SS is not used for SPI communication because it is used to control the direction of the RS485 transceiver; you can use any digital I/O line as a /SS signal. RESOURCE and the access control functions GET() and RELEASE().

The next section describes the registers that configure and control the QScreen Controller’s SPI. In connection with the need for rapid response by the central location for all types of heating systems failures and malfunctions substations located in many parts of the city, MEC Kolobrzeg decided to execute a remote system monitoring and control of heating systems.The monitoring system is based on Citect SCADA visualization software v. 6.0. This software is a standard for the entire heating system to monitor the MEC Kolobrzeg.Delivered new server running under operating system Windows Server 2003. Visualization of the nodes attached to an existing application that supports the entire heating plant. We tried to build an organic system so that whoever gets a TXtemp, TXsoil sensor or a bridge for RS232 or ModBus sensors and devices like TXdata can immediately use them without wasting time in configurations (and we also took the opportunity to insert some things into our system some "extra" not foreseen by the standards!). After configuring the SPI system to communicate on a properly connected network of devices, sending and receiving data is as simple as writing and reading a register. You can implement the slave select lines by configuring Port A pins as outputs.