SA8803
FIGURE 3: TIMING DIAGRAM
B
P
S
S
DATA
CLK
BIT 11
1
2
3
4
5
6
7
8
CLK
T
0
F
=
8 x S
CLK
0
DR-00596
The acceptable Clock pulse Period (TO) may be calculated as follows:
The rising edge may not shift more than half a bit period (BP), therefore:
11 x BP - (½ x BP) <11 x 8 x TO < 11 x BP (½ x BP)
Therefore:
11 x 8 x TO = 11 x BP ± (½ x BP)
(BP ÷ 8)
.·.
.·.
TO = (BP ÷ 8) ±
22
TO = (BP ÷ 8) ± 4,55%
The acceptable frequency for the clock FO is calculated as follows:
1
FO =
TO
1
.·. FO =
(BP ÷ 8) (1 ± 1 )
22
But because:
1
BR x 8 =
(BP ÷ 8)
where BR = Baud Rate
22
FO = (BR x 8) x
(1 ± 22)
.·.
FO = BR x 8 ± 4.55%
The SA8803 has been specified for an external clock frequency of 8 times the Baud
Rate ± 3%.
6/10
sames
SAMES [ SAMES ]
