IBM PowerPC 405GP User Manual page 197

26:30 UDIV UART Internal Clock Divisor UDIV specifies the divisor of the CPU clock
00000 Divide by 1 frequency used to derive a UART serial
00001 Divide by 2 clock frequency. For example, if the CPU is
00010 Divide by 3 running at 200M Hz, a divider value of 20
sets the serial clock frequency to 10MHz.
Note:
The maximum serial clock
frequency is less than 1/2
x
OPS
11110 Divide by 31 frequency
11111 Divide by 32
31
...
Reserved
....
7-14 PPC405GP User's Manual Preliminary