R8C/38T-A Group
19. Serial Interface (UART0)
Under development Preliminary document
Specifications in this document are tentative and subject to change.
R01UH0241EJ0010 Rev.0.10
Page 395 of 730
Aug 05, 2011
19.3.2.2
Bit Rate
In clock asynchronous serial I/O mode, the bit rate is obtained by dividing the frequency with the U0BRG
register and further dividing it by 16.
The value to be set in the U0BRG register is calculated as follows:
When an internal clock is selected
When an external clock is selected
Note:
1. This applies when the high-speed on-chip oscillator is selected as the system clock and bits FRA22 to FRA20 in
the FRA2 register are set to 000b (divide-by-2 mode). For details on the accuracy of the high-speed on-chip
Table 19.8
Setting Example for Clock Asynchronous Serial I/O Mode (Internal Clock Selected)
Bit Rate
(bps)
U0BRG
Count
Source
System Clock = 20 MHz
System Clock = 18.432 MHz
(1)System Clock = 8 MHz
Value Set
in U0BRG
Register
Actual
Rate (bps)
Setting
Error
(%)
Value Set
in U0BRG
Register
Actual
Rate (bps)
Setting
Error
(%)
Value Set
in U0BRG
Register
Actual
Rate (bps)
Setting
Error
(%)
1200
f8
129 (81h)
1201.92
0.16
119 (77h)
1200.00
0.00
51 (33h)
1201.92
0.16
2400
f8
64 (40h)
2403.85
0.16
59 (3Bh)
2400.00
0.00
25 (19h)
2403.85
0.16
4800
f8
32 (20h)
4734.85
-1.36
29 (1Dh)
4800.00
0.00
12 (0Ch)
4807.69
0.16
9600
f1
129 (81h)
9615.38
0.16
119 (77h)
9600.00
0.00
51 (33h)
9615.38
0.16
14400
f1
86 (56h)
14367.82
-0.22
79 (4Fh)
14400.00
0.00
34 (22h)
14285.71
-0.79
19200
f1
64 (40h)
19230.77
0.16
59 (3Bh)
19200.00
0.00
25 (19h)
19230.77
0.16
28800
f1
42 (2Ah)
29069.77
0.94
39 (27h)
28800.00
0.00
16 (10h)
29411.76
2.12
38400
f1
32 (20h)
37878.79
-1.36
29 (1Dh)
38400.00
0.00
12 (0Ch)
38461.54
0.16
57600
f1
21 (15h)
56818.18
-1.36
19 (13h)
57600.00
0.00
8 (08h)
55555.56
-3.55
115200
f1
10 (0Ah) 113636.36
-1.36
9 (09h) 115200.00
0.00
—
Value set in U0BRG register =
fj
Bit rate × 16
fj: Frequency of U0BRG count source (f1, f8, f32, or fC1)
- 1
Value set in U0BRG register =
fEXT
Bit rate × 16
fEXT: Frequency of U0BRG count source (external clock)
- 1