Panasonic MN103001G/F01K User Manual
Page 348
Serial Interface
13-46
Division ratio 1 = INT (IOCLK frequency / bit rate/127) + 1
Division ratio 2 = INT (IOCLK frequency / bit rate/division ratio 1 + 0.5)
Subtract 1 from the value for division ratio 2 that was derived through the above equations, and write the result in
SC3TIM.
If the value of division ratio 1 is 2 or higher, timer 2 or timer 8 must be used to divide the clock. Set SC3CK1 and
0 in the serial 3 control register SC3CTR to "01", and then set the control registers of timer 2 so that the clock is
divided by the value of division ratio 1. (Otherwise, set SC3CK1 and 0 in the serial 3 control register SC3CTR to
"11", and then set the control registers of timer 8 so that the clock is divided by the value of division ratio 1.)
If the value of division ratio 1 is 1, set SC3CK1 and 0 in the serial 3 control register SC3CTR to "00" and select
IOCLK.
The error versus the actual bit rate is calculated as follows:
Bit rate error = ABS (division ratio 1 x division ratio 2 x bit rate / IOCLK frequency – 1)
For example, when a 15 MHz IOCLK signal is used and transfer is conducted at a rate of 38.4 kbit/s, the timer
function is used to divide the clock signal. According to the equations shown above, division ratio 1 is 4 and
division ratio 2 is 98.
Set TM2BR = 3 in the timer 2 base register and SC3TIM = 97 in the serial 3 timer register, and set SC3CK1 and 0
to "01".
According to the equation shown above, the bit rate error is 0.35 %.
Tables 13-4-2 through 13-4-4 show typical examples.
Table 13-4-2
Bit Rates (1) (When IOCLK = 15 MHz)
Bit rate (bit/s)
Division ratio 1
Division ratio 2
Bit rate error
230 400
1
65
0.16 %
115 200
2
65
0.16 %
56 000
3
89
0.32 %
38 400
4
98
0.35 %
19 200
7
112
0.35 %
9 600
13
120
0.16 %
4 800
25
125
0.00 %
2 400
50
125
0.00 %
1 200
99
126
0.21 %
600
197
127
0.08 %
300
394
127
0.08 %
150
788
127
0.08 %
Note: When using a timer to divide the clock signal, subtract 1 from the value of division ratio 1 as derived from
the equations on the top of this page, and write the result in the timer base register. For details, refer to the
chapter on the 8-bit timers.