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The M bit, with mask 0x10, determines whether eight or nine bits total are transmitted with each byte, regardless of whether or not the most-significant bit is a parity bit. Alternatively, the if the SPI interrupts are enabled, the SPI interrupt handler determines what caused the interrupt by reading the SPSR register to see which of the three status bits is set. The PE bit, with mask 0x02, determines whether the most-significant bit in each byte is used as a parity bit. The above parity settings will also determine how incoming data is interpreted (whether the most significant bit is considered a parity bit or part of the data being transmitted, and how many bits total to expect in each byte). For seven data bits with a parity bit, M would be cleared (equal to zero), and PE would be set in order to make the most-significant bit of a normal eight-bit byte be used by the serial port as a parity bit.

When PE is cleared (equal to zero), the most-significant bit of each transmitted character will be a data bit. A logic-low start bit marks the start of a character, followed by 5 to 8 data bits per character. The BAUD routine described at the start of this subsection configures the baud rate of each of the Serial1 and Serial2 channels. Because we chose the default baud rate (which the terminal is presumably already set for), you can simply move the serial cable from the Serial Port 1 connector to the Serial Port 2 connector on the Docking Panel to complete the change to the new port. In this case, cable connections may be made to Serial 2 on either the 10-pin PDQ Board Serial Communications Header, or the Docking Panel’s 10-pin right-angle Serial Header, or the Docking Panel’s Serial2 DB-9 Connector. By default, the RS485 connections are not brought out to the Docking Panel’s DB-9 Serial1 Connector. Table 9-6 Serial Cable Connections. The most widely used protocol is RS232, a full duplex protocol with a single-ended bipolar voltage swing on the serial cable. RS232’s greatest benefit is its universality; practically all personal computers can use this protocol to send and receive serial data.

This section describes the driver routines that control the RS485 transceiver, and presents some ideas that may prove useful in designing a multi-drop data exchange protocol. RS485 uses the same differential signaling scheme as RS422, rs485 cable and hence has the same superior signal-to-noise characteristics and range described above. RS-485 standard conformant drivers provide a differential output of a minimum 1.5 V across a 54-Ω load, whereas standard conformant receivers detect a differential input down to 200 mV. That places a 120 Ω resistor across the RS485 differential line at the driver chip. This allows for basic error detection, in that if noise on the transmission line causes one bit to be received incorrectly, either received as a '0' when transmitted as a '1' or vice-versa, the error would be detected due to the count of '1' bits in the byte being odd when it is expected to be even, or vice-versa depending on the parity checking settings. Parity checking is not often used, because it is not a robust method of error detection. If two bits are received incorrectly, the error will go unnoticed by parity checking. If PT is set, all transmitted bytes with a parity bit will have an odd number of total '1' bits.

Once you have selected the appropriate firmware, select the "??(O)" button. Also, several non-serial interrupts can stack up; if they have higher priority than the serial interrupts, they will be serviced before the Serial2 interrupt routine, and again a serial input or output bit may be lost. The Serial1 and Serial2 ports are is supported by the HCS12's dual on-chip hardware UARTs, and do not require interrupts to work properly. The Control-C Glossary contains a list of functions that temporarily disable interrupts, and the glossary entries give further information regarding how long interrupts are disabled. SERIAL.h header file, and are described in detail in the C Glossary. These signals are described in detail below. It has a special capacitive sensor designed by us, efficient and of good precision, waterproof, resistant to oxidation and not subject to variations due to salinity and soil composition: better than this there are only the "extraction pressure" sensors (which we do not propose because they are not durable and also the sensor alone costs hundreds of euros).