3 synchronization error – Texas Instruments MSP430x1xx User Manual
Page 244
Baud Rate Considerations
12-28
Table 12–6.Commonly Used Baud Rates, Baud Rate Data, and Errors
Divide by
ACLK (32,768 Hz)
MCLK (1,048,576 Hz)
Baud
Rate
ACLK
MCLK
UBR1
UBR0
UMOD
Max.
TX
Error %
Max.
RX
Error %
Synchr.
RX
Error %
UBR1
UBR0
UMOD
Max. TX
Error%
Max. RX
Error %
75
436.91
13,981
1
B4
FF
–0.1/0.3
–0.1/0.3
±
2
36
9D
FF
0/0.1
±
2
110
297.89
9532.51
1
29
FF
0/0.5
0/0.5
±
3
25
3C
FF
0/0.1
±
3
150
218.45
6990.5
0
DA
55
0/0.4
0/0.4
±
2
1B
4E
FF
0/0.1
±
2
300
109.23
3495.25
0
6D
22
–0.3/0.7
–0.3/0.7
±
2
0D
A7
00
–0.1/0
±
2
600
54.61
1747.63
0
36
D5
– 1/1
– 1/1
±
2
06
D3
FF
0/0.3
±
2
1200
27.31
873.81
0
1B
03
– 4/3
– 4/3
±
2
03
69
FF
0/0.3
±
2
2400
13.65
436.91
0
0D
6B
6/3
– 6/3
±
4
01
B4
FF
0/0.3
±
2
4800
6.83
218.45
0
06
6F
– 9/11
– 9/11
±
7
0
DA
55
0/0.4
±
2
9600
3.41
109.23
0
03
4A
– 21/12
– 21/12
±
15
0
6D
03
–0.4/1
±
2
19,200
54.61
0
36
6B
–0.2/2
±
2
38,400
27.31
0
1B
03
– 4/3
±
2
76,800
13.65
0
0D
6B
– 6/3
±
4
115,200
9.10
0
09
08
– 5/7
±
7
The maximum error is calculated for the receive and transmit modes. The
receive-mode error is the accumulated time versus the ideal scanning time in
the middle of each bit. The transmit error is the accumulated timing error
versus the ideal time of the bit period.
The MSP430 USART peripheral interface allows baud rates nearly as high as
the clock rate. It has a low error accumulation as a result of modulating the
individual bit timing. In practice, an error margin of 20% to 30% supports
standard serial communication.
12.7.3 Synchronization Error
The synchronization error, shown in Figure 12–29, results from the
asynchronous timing between the URXD pin data signal and the internal clock
system. The receive signal is synchronized with the BRSCLK clock. The
BRSCLK clock is sixteen to thirty-one times faster than the bit timing, as
described.
BRSCLK = BRCLK
for
N
≤
1F
BRSCLK = BRCLK/2
for
20h
≤
N
≤
3Fh
BRSCLK = BRCLK/4
for
40h
≤
N
≤
7Fh
BRSCLK = BRCLK/8
for
80h
≤
N
≤
FFh
BRSCLK = BRCLK/16
for
100
≤
N
≤
1FF
BRSCLK = BRCLK/32
for
200
≤
N
≤
3FFh
BRSCLK = BRCLK/64
for
400
≤
N
≤
7FFh
BRSCLK = BRCLK/128
for
800h
≤
N
≤
FFFh
BRSCLK = BRCLK/256
for
1000h
≤
N
≤
1FFFh
BRSCLK = BRCLK/512
for
2000h
≤
N
≤
3FFFh
BRSCLK = BRCLK/1024
for
4000h
≤
N
≤
7FFFh
BRSCLK = BRCLK/2048
for
8000h
≤
N
≤
FFFFh