TLH6750 – 33

FIGURE 30 A simple carrier amplitude detector with output low when carrier is detected

TLH6750 – 34

FIGURE 31 A simple linear analog audio transmitter and receiver are shown

The carrier and 16V inputs are derived from the carrier detector of

Figure 30

The remaining 2 LM339 comparators may be used to build the carrier detector circuit

Communication and System

sion in a system Its first purpose is to put data in a base-

band digital form that is more easily recognized as a real

message at the receive end Secondly it incorporates en-

coding techniques to ensure that noise induced errors do

not easily occur and when they do they can always be

detected Lastly the software algorithms that are used on

the receive end to decode incoming data prevent the recep-

tion of noise induced ‘‘phantom’’ messages and insure the

recovery of real messages from an incoming bit stream that

has been altered by noise

2

System protocol the manner in which messages are co-

ordinated between nodes in a system Its first purpose is to

ensure message retransmission to correct errors (hand-

shake) Secondly it coordinates messages for maximum uti-

lization and efficiency on the network Lastly it ensures that

messages do not collide on the network Common system

protocols include master-slave carrier detect multiple ac-

cess and token passing Token passing and master slave

have been found to be the most useful since they are inher-

ently collision free

Both protocols usually reside as software in a single micro-

controller that is connected to the LM18932893 IO In any

case some sort of intelligence is needed to process incom-

ing and outgoing messages UARTs have no usefulness in

18