Page 859 - Mechanical Engineers' Handbook (Volume 2)

850 Mechatronics

bits for the exponent and sign). Double-precision numbers can range from 10 308 to 10 308
with 13–16 digits of accuracy.

4.3 Microcomputers
Microprocessors often refer to the CPU described above. Most microprocessors contain some
memory in the form of registers. Microcomputers contain microprocessors connected to other
devices by a common data bus. The data bus is a series of conductors that allow information
to flow between each subsystem. The other devices can include input/output (I/O) devices
such as monitors and keyboards or additional memory devices or I/O devices such as analog-
to-digital (A/D) converters. A microcontroller is just enough microcomputer on a chip to
do a specific control job. For example, a microcontroller could be a microprocessor with
some digital I/O to control a home security system.

5 TRANSFER OF DIGITAL DATA
Digital data can be transferred in several ways. The most common methods are parallel and
serial data transfer. Parallel communication transfers several bits at the same time along
separate conductors. In serial communication data bits are sent one after the other along a
single conductor. There are two types of serial communication: synchronous and asynchro-
nous.

5.1 Parallel Data Transfer

In parallel data transfer all bits occur simultaneously on a set of data lines. Each bit is placed
on each data line by the transmitting digital system and then can be read by the receiving
digital system. The advantage of parallel communication is that it is relatively fast (relative
to serial communication) because several bits of data can be transferred at the same time.
The disadvantage is that several conductors are required. See Fig. 34.

5.2 Serial Data Transfer

In serial data transfer a sequence of bits, or train of pulses, occur on a single data line, as
shown in Fig. 35.

Digital system

1
Data 0 Four-bit parallel interface
1
1

P4 P3 P2 P1 P0
Microcontroller

Figure 34 Four-bit parallel transfer of digital data.