
R8C/3GM Group
22. Serial Interface (UART2)
R01UH0284EJ0100 Rev.1.00
Aug 09, 2011
Figure 22.8
Receive Timing in UART Mode
22.4.1
Bit Rate
In UART mode, the bit rate is the frequency divided by the U2BRG register divided by 16.
Table 22.8 lists the
Note:
1. For the high-speed on-chip oscillator, the correction value in the FRA4 register should be written into the FRA1
register and the correction value in the FRA5 register should be written into the FRA3 register.
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 the precision of the high-speed on-chip oscillator,
Table 22.8
Bit Rate Setting Example in UART Mode (Internal Clock Selected)
Bit Rate
(bps)
U2BRG
Count
Source
System Clock = 20 MHz
System Clock = 18.432 MHz
(1)System Clock = 8 MHz
U2BRG
Setting
Value
Actual Time
(bps)
Setting
Error
(%)
U2BRG
Setting
Value
Actual Time
(bps)
Setting
Error
(%)
U2BRG
Setting
Value
Actual
Time
(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
D0
D1
D7
Start bit
Reception starts when a transfer clock
is generated at the falling edge
of the start bit.
“L” is determined.
Receive data taken in
U2BRG
count source
RE bit in
U2C1 register
RXD2
Transfer clock
RI bit in
U2C1 register
RTS2
Stop bit
The above applies when:
PRYE bit in U2MR register = 0 (parity disabled)
STPS bit in U2MR register = 0 (one stop bit)
CRD bit in U2C0 register = 0 (CTS2/RTS2 function enabled), CRS bit = 1 (RTS2 function selected)
IR bit in
S2RIC register
Set to 0 when an interrupt request is acknowledged or by a program.
Data transfer from UART2 receive register
to U2RB register
Receive Timing Example When Transfer Data is 8 Bits Long (Parity Disabled, One Stop Bit)