Content originally posted in LPCWare by DF9DQ on Sat Mar 05 04:25:05 MST 2016
The USART's offer the oversampling ratio OSR as an additional degree of freedom. Default is 16x oversampling, but slightly smaller values are no problem as long as the peer device has a reasonable baud rate accuracy.
Assuming a 12 MHz main clock, you get 12M/100k = 120, 12M/115k2 = 104.17, 12M/9k6 = 1250
104.17 = 8 * 13 (104, 0.16% error)
120 = 8 * 15 (no error)
1250 = 8 * 12 * 13 (1248, 0.16% error)
Leave the UART fractional generator disabled.
UARTCLKDIV = 1
USART0: OSR = 12, BRG = 7
USART1: OSR = 14, BRG = 7
USART2: OSR = 12, BRG = 95
Moving the common factor 8 to UARTCLKDIV may yield slightly lower power consumption.