Modulation is based on the UCBRSx setting as shown in Table 11–2. A 1 in the
table indicates that m = 1 and the corresponding BITCLK period is one BRCLK
period longer than a BITCLK period with m = 0. The modulation wraps around
after 8 bits but restarts with each new start bit.
Table 11–2. BITCLK Modulation Pattern
UCBRSx Bit0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7
     0 0 0 0 0 0 0 0 0
     1 0 1 0 0 0 0 0 0
     2 0 1 0 0 0 1 0 0
     3 0 1 0 1 0 1 0 0
     4 0 1 0 1 0 1 0 1
     5 0 1 1 1 0 1 0 1
     6 0 1 1 1 0 1 1 1
     7 0 1 1 1 1 1 1 1

如果是3的话就是bit2咯？有3个1     4的话是bit7？  是这样理解的么？  最后一位总是设置0是不是好设置点呀？因为这是datasheet里的呀。。