USART Operation: UART Mode
17-11
USART Peripheral Interface, UART Mode
17.2.6 USART Baud Rate Generation
The USART baud rate generator is capable of producing standard baud rates
from non-standard source frequencies. The baud rate generator uses one
prescaler/divider and a modulator as shown in Figure 17−7. This combination
supports fractional divisors for baud rate generation. The maximum USART
baud rate is one-third the UART source clock frequency BRCLK.
Figure 17−7. MSP430 Baud Rate Generator
Bit Start
mX
BRCLK
8
8
UCLKI
ACLK
SMCLK
SMCLK
11
BITCLK
10
01
00
20
27
28
215
Compare (0 or 1)
Modulation Data Shift Register
(LSB first)
16−Bit Counter
Q0
............
Q15
m0
m7
...
...
8
UxBR1
UxBR0
Toggle
FF
N =
R
R
R
UxMCTL
+0 or 1
SSEL1 SSEL0
Timing for each bit is shown in Figure 17−8. For each bit received, a majority
vote is taken to determine the bit value. These samples occur at the N/2−1,
N/2, and N/2+1 BRCLK periods, where N is the number of BRCLKs per
BITCLK.
Figure 17−8. BITCLK Baud Rate Timing
N/2
Bit Start
BRCLK
Counter
BITCLK
N/2−1 N/2−2
1
N/2
N/2−1
1
N/2
N/2−1
N/2−2
0
N/2
N/2−1
1
INT(N/2) + m(= 0)
INT(N/2) + m(= 1)
1
0
N/2
Bit Period
NEVEN: INT(N/2)
NODD : INT(N/2) + R(= 1)
m: corresponding modulation bit
R: Remainder from N/2 division
Majority Vote:
(m= 0)
(m= 1)
Summary of Contents for MSP430x4xx Family
Page 1: ...MSP430x4xx Family 2007 Mixed Signal Products User s Guide SLAU056G ...
Page 2: ......
Page 6: ...vi ...
Page 114: ...3 76 RISC 16 Bit CPU ...
Page 304: ...5 20 FLL Clock Module ...
Page 340: ...7 8 Supply Voltage Supervisor ...
Page 348: ...8 8 16 Bit Hardware Multiplier ...
Page 372: ...9 24 32 Bit Hardware Multiplier ...
Page 400: ...10 28 DMA Controller ...
Page 428: ...13 10 Basic Timer1 ...
Page 466: ...15 24 Timer_A ...
Page 522: ...17 30 USART Peripheral Interface UART Mode ...
Page 544: ...18 22 USART Peripheral Interface SPI Mode ...
Page 672: ...23 12 Comparator_A ...
Page 692: ...24 20 LCD Controller ...
Page 746: ...26 28 ADC12 ...