The DWOM bit (port D wired-or mode) should always be set to 0. Setting DWOM to 1 takes away the processor’s ability to pull the Port D signals high unless there is a pull-up resistor on each bit of the port. 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. All of this allows you to speed up the VFD that controls the speed of that water pump. With your RS485 network, you can remotely monitor and control that pump from a control center. Let’s say you were monitoring a water pump filling a vessel. Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. The interface can be used to support analog to digital and digital to analog converters, networks of many computers controlled by a single master, or networks of devices controlled by several coordinated masters. Without termination resistors, reflections of fast driver edges can cause multiple data edges that can cause data corruption.

The BufferToSPI() function implements fast data transfer from a specified buffer in the controller’s memory to an SPI device. If SPIF is set, reading the received data or initiating a new data transfer automatically clears the SPIF bit. Then reading the data that was received (by reading the SPDR) or initiating a new data transfer (by writing to the SPDR) automatically clears the SPIF flag. After a data transfer is initiated by writing to the SPDR data register, the processor may poll the SPSR status register until the SPIF flag is set. The two lowest order bits in the SPCR control register, named SPR1 and SPR0, determine the data exchange frequency expressed in bits per second; this frequency is also known as the baud rate. The SPIF is set when a data transfer is complete, and is cleared by a read of the SPSR status register, followed by a read or write to the SPDR data register. This setting is only relevant for the master device, what is rs485 cable as it is the master’s clock which drives the transfer. The CPOL and CPHA bits configure the synchronous clock polarity and phase and specify when valid data is present on the MISO and MOSI data lines.

0.2 is the minimum recommended voltage difference that receivers use to detect a change in polarity. The EIA once labeled all its standards with the prefix "RS" (Recommended Standard), but the EIA-TIA officially replaced "RS" with "EIA/TIA" to help identify the origin of its standards. The recommended arrangement of the wires is as a connected series of point-to-point (multidropped) nodes, i.e. a line or bus, not a star, ring, or multiply connected network. It is important to note that when the CPHA bit is 0, the /SS line must be de-asserted and re-asserted between each successive data byte exchange (68HC11 Reference Manual, Section 8.3.2). If the CPHA bit is 1, the /SS line may be tied low between successive transfers. Section 4 defines the electrical characteristics of the generator (transmitter or driver), receiver, transceiver, and system. These characteristics include: definition of a unit load, voltage ranges, open-circuit voltages, thresholds, and transient tolerance. Because a mark (logic 1) condition is traditionally represented (e.g. in RS-232) with a negative voltage and space (logic 0) represented with a positive one, A may be considered the non-inverting signal and B as inverting.

A (green, negative) is higher than B (red, positive). For an off, mark or logic 1 state, the driver's A terminal is negative relative to the B terminal. In contrast to RS-422, which has a driver circuit which cannot be switched off, RS-485 drivers use three-state logic allowing individual transmitters to be deactivated. Pre-coded device drivers configure the SPI for a standard data format, and it is easy to customize a data format and baud rate for your application. TSB-89A, Application Guidelines for TIA/EIA-485-A does not recommend using star topology. If a star configuration is unavoidable, special RS-485 repeaters are available which bidirectionally listen for data on each span and then retransmit the data onto all other spans. This bit should be set only after all other SPI configuration is complete. The WCOL flag is set when a write collision occurs. The equipment located along a set of RS-485 wires are interchangeably called nodes, stations or devices.