Fujitsu FR81S User Manual
CHAPTER 40: MULTI-FUNCTION SERIAL INTERFACE
5. Operation of UART
FUJITSU SEMICONDUCTOR LIMITED
CHAPTER : MULTI-FUNCTION SERIAL INTERFACE
FUJITSU SEMICONDUCTOR CONFIDENTIAL
168
(Example) Bus clock 20MHz, Target baud rate value 153600 bps
Reload value
= (20 ∗ 1000000) / 153600 - 1 = 129
Baud rate (calculated value) = (20 ∗ 1000000) / (129 + 1) = 153846 bps
Error (%)
= (153846 - 153600)/ 153600 ∗ 100 = 0.16(%)
Notes:
⋅
Set the reload value to "0" to stop the reload counter.
⋅
If the reload value is an even number, the "L" width of the reception serial clock is 1 bus clock longer
than "H" width. If it is an odd number, the "H" and "L" widths of the serial clock are equal.
⋅
Set the reload value to 4 or higher. A normal data reception operation, however, could not be achieved for
some baud rate error and reload value settings.
Allowed Baud Rate Error Range at Reception
This section explains the amount of the destination baud rate error that can be allowed at reception.
The baud rate error at reception should be set within the allowed error range by using following formula.
Figure 5-19 Allowed Baud Rate Range at Reception
UART
transfer rate
Start bit0 bit1 bit7 Parity Stop
Sampling
▽ ▽ ▽ ▽ ▽ ▽
Allowed minimum
transfer rate
FL
1data・frame (11×FL)
Start bit0 bit1 bit7 Parity Stop
FLmin
Allowed maximum
transfer rate
Start bit0 bit1 bit7 Parity Stop
Flmax
As shown in the Figure the counter set by the BGR register will determine the sampling timing of the
reception data after having detected a start bit. A normal reception operation can be achieved if the last data
(stop bit) have been completed on time at this sampling timing.
In theory, the following is expected when this is applied to 11-bit reception.
If the margin of sampling timing is 1 clock of bus clock (φ), the allowed minimum transfer rate (FLmin)
would be calculated as follows.
FLmin = (11bit ∗ (V+1)
−
(V+1) / 2 +2) / φ = (21V+25) / 2φ (s)
V: Reload value φ: Bus clock
Therefore, the allowed maximum baud rate (BGmax) at the destination would be calculated as follows.
BGmax = 11/FLmin = 22φ / (21V+25) (bps)
V: Reload value φ: Bus clock
When the allowance and maximum transfer rate (FLmax) receives the data, sampling is done in the starting
point of receive data in the 11th bit.
Therefore, the allowance and maximum transfer rate (FLmax) is as follows.
MB91520 Series
MN705-00010-1v0-E
1481