National CP3BT26 User Manual
173
www.national.com
CP3
BT26
22.4.2
Synchronous Mode
Synchronous mode is only available for the UART0 module.
When synchronous mode is selected and the UCKS bit is
set, the UART operates from a clock received on the CKX
pin. When the UCKS bit is clear, the UART uses the clock
from the internal baud rate generator which is also driven on
the CKX pin. When the internal baud rate generator is used,
the equation for calculating the baud rate is:
When synchronous mode is selected and the UCKS bit is
set, the UART operates from a clock received on the CKX
pin. When the UCKS bit is clear, the UART uses the clock
from the internal baud rate generator which is also driven on
the CKX pin. When the internal baud rate generator is used,
the equation for calculating the baud rate is:
where BR is the baud rate, SYS_CLK is the System Clock,
N is the value of the baud rate divisor + 1, and P is the pres-
caler divide factor selected by the value in the UnPSR reg-
ister. Oversampling is not used in synchronous mode.
N is the value of the baud rate divisor + 1, and P is the pres-
caler divide factor selected by the value in the UnPSR reg-
ister. Oversampling is not used in synchronous mode.
Use the same procedure to determine the values of N and
P as in the asynchronous mode. In this case, however, only
integer prescaler values are allowed.
P as in the asynchronous mode. In this case, however, only
integer prescaler values are allowed.
BR
SYS_CLK
2
N
P
×
×
(
)
-----------------------------
=
Table 71
Baud Rate Programming
Baud
Rate
SYS_CLK = 48 MHz
SYS_CLK = 24 MHz
SYS_CLK = 12 MHz
SYS_CLK = 10 MHz
O
N
P
%err
O
N
P
%err
O
N
P
%err
O
N
P
%err
300
16
2000
5.0
0.00
16
2000
2.5
0.00
16
1250
2.0
0.00
13
1282
2.0
0.00
600
16
2000
2.5
0.00
16
1250
2.0
0.00
16
1250
1.0
0.00
13
1282
1.0
0.00
1200
16
1250
2.0
0.00
16
1250
1.0
0.00
16
625
1.0
0.00
13
641
1.0
0.00
1800
7
401
9.5
0.00
8
1111
1.5
0.01
12
101
5.5
0.01
12
463
1.0
0.01
2000
16
1500
1.0
0.00
16
750
1.0
0.00
16
250
1.5
0.00
16
125
2.5
0.00
2400
16
1250
1.0
0.00
16
625
1.0
0.00
16
125
2.5
0.00
9
463
1.0
0.01
3600
8
1111
1.5
0.01
12
101
5.5
0.01
11
202
1.5
0.01
11
101
2.5
0.01
4800
16
625
1.0
0.00
16
125
2.5
0.00
10
250
1.0
0.00
7
119
2.5
0.04
7200
12
101
5.5
0.01
11
303
1.0
0.01
11
101
1.5
0.01
10
139
1.0
0.08
9600
16
125
2.5
0.00
10
250
1.0
0.00
10
125
1.0
0.00
7
149
1.0
0.13
14400
11
202
1.5
0.01
11
101
1.5
0.01
14
17
3.5
0.04
14
33
1.5
0.21
19200
10
250
1.0
0.00
10
125
1.0
0.00
10
25
2.5
0.00
16
13
2.5
0.16
38400
10
125
1.0
0.00
10
25
2.5
0.00
16
13
1.5
0.16
8
13
2.5
0.16
56000
7
49
2.5
0.04
13
33
1.0
0.10
13
11
1.5
0.10
7
17
1.5
0.04
115200
7
17
3.5
0.04
13
16
1.0
0.16
13
8
1.0
0.16
7
5
2.5
0.79
128000
15
25
1.0
0.00
15
5
2.5
0.00
11
1
8.5
0.27
12
1
6.5
0.16
230400
13
16
1.0
0.16
13
8
1.0
0.16
13
4
1.0
0.16
11
4
1.0
1.36
345600
9
1
15.5
0.44
10
7
1.0
0.79
10
1
3.5
0.79
460800
13
8
1.0
0.16
13
4
1.0
0.16
13
2
1.0
0.16
11
2
1.0
1.36
576000
8
7
1.5
0.79
12
1
3.5
0.79
14
1
1.5
0.79
7
1
2.5
0.79
691200
10
7
1.0
0.79
10
1
3.5
0.79
7
1
2.5
0.79
806400
7
1
8.5
0.04
15
2
1.0
0.79
10
1
1.5
0.79
921600
13
4
1.0
0.16
13
2
1.0
0.16
13
1
1.0
0.16
1105920
11
4
1.0
1.36
11
2
1.0
1.36
9
1
1.0
0.47
1382400
10
1
3.5
0.79
7
1
2.5
0.79
1536000
9
1
3.5
0.79
8
2
1.0
2.34