21-12-2012, 05:54 PM
Line Coding, Modem, RS232 interfacing sequences.
Line Coding, Modem.ppt (Size: 349 KB / Downloads: 25)
DC Components
Residual direct-current (dc) components or zero frequencies are undesirable
Some systems do not allow passage of a dc component; may distort the signal and create output errors
DC component is extra energy and is useless
Self-Synchronization
Includes timing information in the data being transmitted to prevent misinterpretation
Polar
Uses two voltage levels, one positive and one negative
Alleviates DC component
Variations
Nonreturn to zero (NRZ)
Return to zero (RZ)
Manchester
Differential Manchester
Return to Zero
In NRZ-I, long strings of 0s may still be a problem
May include synchronization as part of the signal for both 1s and 0s
How?
Must include a signal change during each bit
Uses three values: positive, negative, and zero
1 bit represented by positive-to-zero
0 bit represented by negative-to-zero