R01UH0822EJ0100 Rev.1.00
Page 606 of 1041
Jul 31, 2019
RX13T Group
23. Serial Communications Interface (SCIg, SCIh)
23.2.11
Bit Rate Register (BRR)
The BRR register is an 8-bit register that adjusts the bit rate.
As each SCI channel has independent baud rate generator control, different bit rates can be set for each.
shows the relationship between the setting (N) in the BRR register and the bit rate (B) for normal asynchronous mode,
multi-processor communication, clock synchronous mode, smart card interface mode, simple SPI mode, and simple I
2
C
mode.
The BRR register is writable only when the TE and RE bits in the SCR register are 0.
B:
Bit rate (bps)
N:
BRR setting for on-chip baud rate generator (0
N
255)
PCLK:
Operating frequency (MHz)
n and S: Determined by the settings of the SMR and SCMR registers as listed in Table 23.12 and Table 23.13.
Note 1. Adjust the bit rate so that the widths at high and low level of the SCL output in simple I
2
C mode satisfy the I
2
C-bus standard.
Address(es): SCI1.BRR 0008 A021h, SCI5.BRR 0008 A0A1h, SCI12.BRR 0008 B301h
b7
b6
b5
b4
b3
b2
b1
b0
Value after reset:
1
1
1
1
1
1
1
1
Table 23.10
Relationship between N Setting in BRR Register and Bit Rate B
Mode
SEMR Settings
BRR Setting
Error (%)
BGDM bit
ABCS bit
Asynchronous,
multi-processor
communication
0
0
0
1
1
0
1
1
Clock synchronous, simple SPI
Smart card interface
Simple I
2
Table 23.11
Calculating Widths at High and Low Level for SCL
Mode
SCL
Formula (Result in Seconds)
I
2
C
High period (minimum value)
Low period (minimum value)
N
PCLK 10
6
64 2
2n 1
–
B
---------------------------------------
1
–
=
Error
PCLK 10
6
B 64
2
2n 1
–
N 1
+
----------------------------------------------------------------
1
–
100
=
N
PCLK 10
6
32 2
2n 1
–
B
---------------------------------------
1
–
=
Error
PCLK 10
6
B 32
2
2n 1
–
N 1
+
----------------------------------------------------------------
1
–
100
=
N
PCLK 10
6
16 2
2n 1
–
B
---------------------------------------
1
–
=
Error
PCLK 10
6
B 16
2
2n 1
–
N 1
+
----------------------------------------------------------------
1
–
100
=
N
PCLK 10
6
8 2
2n 1
–
B
-----------------------------------
1
–
=
N
PCLK 10
6
S 2
2n 1
+
B
------------------------------------
1
–
=
Error
PCLK 10
6
B S
2
2n 1
+
N 1
+
--------------------------------------------------------------
1
–
100
=
N
PCLK 10
6
64 2
2n 1
–
B
---------------------------------------
1
–
=
N 1
+
4
2
2n 1
–
7
1
PCLK 10
6
--------------------------------
N 1
+
4
2
2n 1
–
8
1
PCLK 10
6
--------------------------------