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Baud Rate Generator
Baud rate generator comprises a circuit that gener-
ates transmission and receiving clocks to determine the
transfer rate of the serial channel.
The input clock to the baud rate generator, φ T0 (fc/
4), φ T2 (fc/16), φ T8 (fc/64), or φ T32 (fc/256) is generated
by the 9-bit prescaler which is shared by the timers. One
UART mode
Transfer rate =
I/O interface mode
Transfer rate =
The relation between the input clock and the source clock (fc) is as follows:
φ T0 =
fc/4
φ T2 = fc/16
φ T8 = fc/64
φ T32 = fc/256
Accordingly, when source clock fc is 12.288 MHz, input clock is φ T2 (fc/16), and frequency divisor is 5, the transfer rate
in UART mode becomes as follows:
Transfer rate =
Table 3.11 (1) shows an example of the transfer rate in UART mode.
Also with 8-bit timer 0, the serial channel can get a transfer rate. Table 3.11 (2) shows an example of baud rate using
timer 0.
Table 3.11 (1) Selection of Transfer Rate (1) (When Baud Rate Generator is Used)
fc [Mhz]
Frequency
Divisor
9.830400
↑
↑
↑
12.288000
↑
14.745600
↑
↑
Note:
Transfer rate in I/O interface mode is 8 times as fast as the values given in the above table.
TOSHIBA CORPORATION
Input clock of baud rate generator
Frequency divisor of baud rate generator
Input clock of baud rate generator
Frequency divisor of baud rate generator
fc/16
5
6
= 12.288 x 10
/16/5/16 = 9600 (bps)
Input Clock
φ T0
(fc/4)
2
76.800
4
38.400
8
19.200
0
9.600
5
38.400
A
19.200
3
76.800
6
38.400
C
19.200
of these input clocks is selected by the baud rate genera-
tor control register BR0CR/BR1CR <BR0CK1, 0/
BR1CK1, 0>.
The baud rate generator includes a 4-bit frequency
divider, which divides frequency by 2 to 16 values to
determine the transfer rate.
How to calculate a transfer rate when the baud rate
generator is used is explained below.
÷ 16
φ T2
(fc/16)
19.200
9.600
4.800
2.400
9.600
4.800
19.200
9.600
4.800
TMP96C141AF
÷ 16
÷ 2
Unit (kbps)
φ T8
φ T32
(fc/64)
(fc/256)
4.800
1.200
2.400
0.600
1.200
0.300
0.600
0.150
2.400
0.600
1.200
0.300
4.800
1.200
2.400
0.600
1.200
0.300
127
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