Renesas H8S Series Hardware Manual page 510

The BRR setting is found from the following formulas.
Asynchronous mode:
ø
N =
64 × 2
2n–1
Clocked synchronous mode:
ø
N =
8 × 2
2n–1
Where B: Bit rate (bit/s)
N: BRR setting for baud rate generator (0 ≤ N ≤ 255)
ø: Operating frequency (MHz)
n: Baud rate generator input clock (n = 0 to 3)
(See the table below for the relation between n and the clock.)
The bit rate error in asynchronous mode is found from the following formula:
Error (%) = {
Rev.6.00 Oct.28.2004 page 482 of 1016
REJ09B0138-0600H
× 10
6
– 1
× B
× 10
6
– 1
× B
n Clock
0 ø
1 ø/4
2 ø/16
3 ø/64
ø × 10
6
(N + 1) × B × 64 × 2
2n–1
SMR Setting
CKS1 CKS0
0 0
0 1
1 0
1 1
– 1} × 100