Datasheet

Section 15 Serial Communication Interface (SCI, IrDA)
Rev.7.00 Mar. 18, 2009 page 711 of 1136
REJ09B0109-0700
15.3.9 Bit Rate Register (BRR)
BRR is an 8-bit register that adjusts the bit rate. As the SCI performs baud rate generator control
independently for each channel, different bit rates can be set for each channel. Table 15.2 shows
the relationships between the N setting in BRR and bit rate B for normal asynchronous mode,
clocked synchronous mode, and Smart Card interface mode. The initial value of BRR is H'FF, and
it can be read or written to by the CPU at all times.
Table 15.2 Relationships between N Setting in BRR and Bit Rate B
Mode Bit Rate Error
Asynchronous
Mode
B =
64 × 2
2n−1
× (N + 1)
φ × 10
6
Error (%) = {
B × 64 × 2
2n−1
× (N + 1)
− 1 } × 100
φ × 10
6
Clocked
Synchronous
Mode
B =
8 × 2
2n−1
× (N + 1)
φ × 10
6
Smart Card
Interface Mode
B =
S × 2
2n+1
× (N + 1)
φ × 10
6
Error (%) = {
B × S × 2
2n+1
× (N + 1)
− 1 } × 100
φ × 10
6
Note: B: Bit rate (bit/s)
N: BRR setting for baud rate generator (0 ≤ N ≤ 255)
φ: Operating frequency (MHz)
n and S: Determined by the SMR settings shown in the following tables.
SMR Setting SMR Setting
CKS1 CKS0 n BCP1 BCP0 S
0 0 0 0 0 32
0 1 1 0 1 64
1 0 2 1 0 372
1 1 3 1 1 256
Table 15.3 shows sample N settings in BRR in normal asynchronous mode. Table 15.4 shows the
maximum bit rate for each frequency in normal asynchronous mode. Table 15.6 shows sample N
settings in BRR in clocked synchronous mode. Table 15.8 shows sample N settings in BRR in
Smart Card interface mode. In Smart Card interface mode, S (the number of basic clock periods in
a 1-bit transfer interval) can be selected. For details, refer to section 15.7.4, Receive Data
Sampling Timing and Reception Margin. Tables 15.5 and 15.7 show the maximum bit rates with
external clock input.