Serial data transmission

The RS-232-C standard defines a serial interface which is commonly used. In its minimum configuration it is possible to transmit data over 15 meters with only three wires. For large distances a modem would be necessary. Data transmission is performed by sending the individual bits of a data byte one after the other. The data bits are enclosed by special bits (start bit, parity bit, stop bit) which provide proper synchronization and error detection in the receiver. The form of the transfer is called the protocol. This protocol defines the baud rate (bits per second = baud), the number of stop bits and an optional parity bit. Figure 8.10 shows an example of transmitted data. A logical 0 is transmitted by a voltage level of +3.. + 12 V and a... 

After the analog signal has been converted to digital form the next step is to make the digital data available to the computer. There are two major modes of signal transmission serial transmission and parallel transmission. 

The serial data transmission mode finds its greatest use in multiple detector/converter systems where data must be sent over moderate to long distances to the computer. The system is easy to implement, has a good noise immunity, and is reliable. The main disadvantage to the serial system is its moderate speed of transmission, which is about 3000 bytes/sec. This relatively low speed of transfer may limit its use in some very high-speed applications e.g. data acquisition of mass... 

Almost every computer made since the original IBM PC has at least one serial port. They are easily identified because they have either a DB-9 male (shown in Figure 2.24) or DB-25 male port. Standard serial ports have a maximum data transmission speed of 57KBps and a maximum cable length of 50 feet. 

The wireless EIT data-transmission scheme (WL-DDTS) generates an 8-bit parallel data set to be converted into the serial data by an encoder [45]. The encoded serial data are then transmitted through the wireless transmission module (Figure 30.6a) and received by the receiver module [45]. 

By using 16-bit encoder/decoder ICs, the direct transmission of 16-bit data is possible (Figure 30.7) and this eliminates the binary adder circuit required for converting 8-bit data to 16-bit data. A 16-bit data-transmission scheme uses 16-bit encoder/decoder ICs (e.g., GL116 [Glolab Corporation, United States]). The transmitter module transmits the 16-bit serial data for the receiver to be converted to 16-bit parallel data. 

Data represented by binary coding on a single t rans-mission line are called serial-coded binary data, or simply rer/n/dntn. A common example of serial data transmission is the computer modem, which is a device for transmitting data between computers by telephone over a single conductor (and a common connection). 

The PC must have a serial port - RS232-C or V.24 - which is connected to a modem to transmit data through the public telephone network. Digital bits are converted by the modem to analog signals and reverse. The public telephone net is used up to the next node - PAD of a public data transmission net. There, the data are bundled into packages and addressed. In addition to this there are further possibilities for transmitting data ... 

External data system serial communication link Bad transmission Limit check with alarm Message validity check Limit check with default... 

The RSW433 and TSW433 radiofrequency modules are used these modules work at a frequency of433 MHz and use AM modulation for data transmission in serial protocol at a speed of 1200 baud. 

The transmission of data between an ADC or DAC and a computer is usually accomplished by sending one byte at a time along a multiway ribbon cable external bus). The IEEE 488 standard bus has been widely used for this purpose, but other buses are also used. As all bits are handled simultaneously this is known as parallel I/O transmission, the data entering or leaving the computer via a parallel port or by direct connection to the computer s internal bus. Alternatively, one bit at a time can be transmitted along a single line serial I/O transmission). Data enter or leave the computer via a serial port, usually an RS-232C. Serial I/O ports are used for... 

Serial output ports (RS-232) are usually provided for serial transmission of data— usually in ASCII code as previously shown in Fig. 5. 

Terminals tied to a computer through RS232C or 20 mA connections are an example of loosely coupled devices. The serial ASCII transmission of data is adequate for applications where dynamics or animation are not a factor (the VT125 and GIGI can be used to a only very limited extent here). This approach has been used in both classes of equipment, our own terminals for example in raster work and Tektronix or IMLAC terminals in vector systems. 

The first block DIV is a frequency divider. This block has 2 modes of operation, the normal mode and the test mode. In the test mode, the UART chip runs 16 times faster than in the normal mode. Also, the transmission data rate of the UART chip is 16 times faster than the receiving rate. Each block is initialized by setting the reset line low by applying a 0 to port MR. The TX block accepts 8-bit parallel data from the microprocessor interface (MP) block and transmits it serially to the RS-232 port through port DOUT. Conversely, the RX block receives serial data input, and sends it in 8-bit parallel format to the MP block. Again, the transmitter runs at 16 times the speed of the receiver. The microprocessor interface (MP) block asynchronously controls the parallel data flow between the RX / TX blocks and the microprocessor data bus. 

In the serial mode, the digital word (number) is sent to the computer one bit at a time. Now a binary counter provides a parallel output since each of the output bits has its own data output channel and the value of each output bit is simultaneously available. To use a serial transmission scheme, this parallel output must be put into serial form. One way to accomplish this is to use a Universal Asynchronous Receiver Transmitter (UART). The detailed operation of the UART will not be given here as it is not germane to the subject of this book. It is sufficient to say that the heart of the UART is a shift register and the shift register is strobed by a signal from the computer that displaces the binary number, bit by bit, sequentially from the register to the computer. 

The parallel data transfer mode is simple to use and allows for greater flexibility than the serial mode. However, it requires numerous connections between the PIA and the A/D Converter, and is, therefore limited to those cases where the converter and computer are very close. This type of transmission is very popular in chromatographs which have a built-in dedicated computer. 

UART Acronym for Universal Asynchronous Receiver/Transmitter. An electronic module that combines the transmitting and receiving circuitry needed for asynchronous transmission over a serial line. Asynchronous transmissions use start and stop bits encoded in the data stream to coordinate communications rather than the clock pulse found in synchronous transmissions. 

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