What is the maximum RS232 data rate that I can generate with ADUC7026?
You should check the ADuC7026 Data sheet.
When Max Core Clock is used (from PLL) then:
Baudrate = 41.78MHz / (16*2*DL)
When DL=1 (Divisor Latch) then Baudrate = 1305625 (I haven't seen any other limitation in the data sheet).
Thank you!