405
0 1 2 3 4 5 6 7 8 9 10111213 1415 0 1 2 3 4 5 6 7 8 9 10111213 1415 0 1 2 3 4 5
Internal
base clock
Receive
data (RxD)
Synchronization
sampling
timing
Data
sampling
timing
8 clocks
16 clocks
Start bit
–7.5 clocks
+7.5 clocks
D0
D1
Figure 13.21 Receive Data Sampling Timing in Asynchronous Mode
The receive margin in asynchronous mode can therefore be expressed as shown in equation 1.
Equation 1:
M = 0.5 –
– (L – 0.5)F –
(1 + F )
×
100%
1
2N
D
–
0.5
N
M: Receive margin (%)
N:
Ratio of clock frequency to bit rate (N = 16)
D:
Clock duty cycle (D = 0 to 1.0)
L:
Frame length (L = 9 to 12)
F:
Absolute deviation of clock frequency
From equation (1), if F = 0 and D = 0.5 the receive margin is 46.875%, as given by equation 2.
Equation 2:
D
= 0.5, F = 0
M
= (0.5 – 1/(2
×
16))
×
100%
= 46.875% (2)
This is a theoretical value. A reasonable margin to allow in system designs is 20–30%.
Summary of Contents for HD6417032
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Page 525: ...490 CK RAS CAS TRp TRc TRcc tRASD1 tRASD2 tCASD3 tCASD2 TRr tCSR Figure 20 18 Self Refresh ...
Page 578: ...543 CK RAS CAS TRp TRc TRcc tRASD1 tRASD2 tCASD3 tCASD2 TRr tCSR Figure 20 62 Self Refresh ...
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