C161U Datasheet, PDF (359/469 Pages) Infineon Technologies AG – Embedded C166 with USB, USART and SSC

C161U
Bootstrap Loader
Note: Function (F_B) does not consider the tolerances of oscillators and other devices
supporting the serial communication.
This baudrate deviation is a nonlinear function depending on the CPU clock and the
baudrate of the host. The maxima of the function (F_B) increase with the host baudrate
due to the smaller baudrate prescaler factors and the implied higher quantization error
(see figure below).
F_B
Ι
2.5%
B_Low
B_High
ΙΙ
B_Host
MCA02260
Figure 113 Baudrate deviation between host and C161U
Minimum baudrate (B_Low in the figure above) is determined by the maximum count
capacity of timer T6, when measuring the zero byte, ie. it depends on the CPU clock.
Using the maximum T6 count 2¹⁶ in the formula the minimum baudrate for f_CPU=20 MHz
is 687 Baud. The lowest standard baudrate in this case would be 1200 Baud. Baudrates
below B_Low would cause T6 to overflow. In this case ASC cannot be initialized properly.
Maximum baudrate (B_High in the figure above) is the highest baudrate where the
deviation still does not exceed the limit, ie. all baudrates between B_Low and B_High are
below the deviation limit. The maximum standard baudrate that fulfills this requirement
is 19200 Baud.
Higher baudrates, however, may be used as long as the actual deviation does not
exceed the limit. A certain baudrate (marked I) in the figure) may eg. violate the deviation
limit, while an even higher baudrate (marked II) in the figure) stays very well below it. This
depends on the host interface.
Data Sheet
359
2001-04-19