Digital Interfaces • An interface links two devices • Interface Standards define: – mechanical specifications - how many wires & connector type – electrical specifications - frequency, amplitude and phase of signal – functional - what does each wire do? – Procedural – how & when to perform functions
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Digital Interfaces An interface links two devices Interface Standards define: – mechanical specifications - how many wires & connector type –electrical.
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Digital Interfaces
• An interface links two devices• Interface Standards define:
– mechanical specifications - how many wires & connector type
– electrical specifications - frequency, amplitude and phase of signal
– functional - what does each wire do?– Procedural – how & when to perform functions
upated 1/2002 2
Serial vs. Parallel• In serial transmission one bit is sent with
each clock pulse.
• Two types of serial transmission:– asynchronous– synchronous
• In parallel transmission multiple bits are sent with each clock pulse. Faster/more expensive
Serial Transmission
0 1 1 0 0 0 1 0
Parallel Transmission01100010
01100010
Serial Transmission
• Asynchronous & Synchronous
• Concerned with timing issues
• How does the receiver know when the bit period begins and ends?
• Small timing difference become more significant over time if no synchronization takes place between sender and receiver
Synchronizations
1 0 0 1 0 0 1 1 1 1 1 0
1 0 0 1 1 0 0 1 1 1 1 1 1 0
time
time
Sen
der
cloc
k R
ecei
ver
cloc
k
Sender data
Received data
Asynchronous Transmission
• Serial communication• Data transmitted 1
character at a time• Character format is 1
start & 1 or more stop bits, plus data of 5-8 bits