Information Technology Reference
In-Depth Information
Data (sent one bit
at a time)
Serial Data
Bus
Device
1
Device
2
Device
1
Device
2
Start
bit sequence
End
bit sequence
Parallel Data
Bus
Device
1
Device
2
Device
1
Device
2
Data
bus
Handshaking line
for synchronising
data (defines when
data is valid on bus)
Handshaking
line
Figure 2.3
Serial/parallel data busses
Data transfer rates
The amount of data that a system can transfer at a time is normally defined either in bits per
second (bps) or bytes per second (B/s). The more bytes (or bits) that can be transferred the
faster the transfer will be. Typically serial busses are defined in bps, whereas parallel busses
use B/s.
The transfer of the data occurs are regular intervals, which is defined by the period of the
transfer clock. This period is either defined as a time interval (in seconds), or as a frequency
(in Hz). For example, if a clock operates at a rate of 1 000 000 cycles per second, its fre-
quency is 1 MHz, and its time interval will be one millionth of a second (1·10
-
6
s).
In general, if
f
is the clock frequency (in Hz), then the clock period (in seconds) will be
1
f
Conversion from clock frequency
to clock time interval
T
=
sec
For example, if the clock frequency is 8 MHz, then the clock period will be:
1
T
=
=
0.00000012
5
sec
Example of a calculation of clock
time interval from clock frequency
6
m
8
·
10
=
0.125
s
The data transfer rate (in bits/second) is defined as:
