advantages and disadvantages of serial and parallel data transmission

Advantages And Disadvantages Of Serial And Parallel Data Transmission Driver IC Converts

Alternatively, the AUXOUT and AUXIN lines can be used to send transmit and receive clocks, for use with synchronous communications schemes.

A differential signal requires two wires, one for noninverted data and the other for inverted data.

It is transmitted over a balanced line, usually twisted-pair wire with a termination resistor at one end (the receiver side).

Advantages And Disadvantages Of Serial And Parallel Data Transmission Driver IC Converts

As shown in Figure 8-17a, a driver IC converts normal logic levels to a differential signal pair for transmission.

A receiver converts the differential signals back to logic levels.

The received data is the difference between the noninverted data (A) and the inverted data (A), as shown in the waveforms of Figure 8-17b.

Note that no ground wire is required between the receiver and transmitter, since the two signal lines are referenced to each other.

However, there is a maximum common-mode voltage (referenced to ground) range on either line of 0.25 V to 6 V, as shown in Table 8-6.

Usually the signal ground is connected between the transmitter and receiver to keep the signals within this common-mode range.

This differential signal scheme enables the use of high data rates (up to 10 Mbps) over long cable lengths (up to 4000 feet) because of its high noise immunity.

If external noise induces a signal on the transmission line, it will be the same on both conductors (A and A).

The receiver will cancel out this common-mode noise by taking the difference between the two lines, as shown in Figure 8-18.

If a single-ended transmission line was used, the noise spikes could show up as false data at the receiver.

The example in Figure 8-18 shows both a positive- and a negative-going noise spike.

Figure 8-18. Differential data lines with common-mode noise.

As with RS-423A, RS-422A can have multiple receivers (10 maximum) on the same line with a single transmitter.

Again, this is basically useful for applications that require broadcasting data from a single source to multiple remote locations.

There are variations in the connectors and pin designations used for RS-422A interconnections.

Most RS-422A interface cards for PCs use 9-pin D-shell connectors, but in lieu of an IBM standard, the pin designations employed vary from one manufacturer to another.

An example of the pin designations on a typical RS-422A interface card for PCs (from Qua Tech Inc.) is shown in Figure 8-19.

Figure 8-19. Pin designations for a typical RS-422A PC interface card.

The signal lines for AUXIN are inputs and can be used to implement a CTS function.

In this way, the RS-422A card can operate like a typical asynchronous RS-232C card in a PC (and use the same control software).