C509-L_97 SIEMENS [Siemens Semiconductor Group], C509-L_97 Datasheet - Page 250

• Manufacturer Part Number: C509-L_97
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

10.3.2 Baud Rates for Correct Synchronization
The automatic baud rate synchronization will work correctly only in a specific range of baud rates,
which depends on the oscillator frequency fosc of the C509-L and the resolution of the timer 0 (T0).
The minimum baud rate (Bd
T0 gets greater than 24556. In this case the value of SFR S0REL, corresponding formula (3), gets
below zero, which leads to a underflow of the S0REL register and therefore to a incorrect baud rate
of the baud rate generator. The formula for calculating this underflow margin is derived from formula
(1) and is reduced to
The theoretical maximum baud rate (Bd
of 1023. In this case formula (1) reduces to
The real maximum baud rate (Bd
T0 at higher baud rates, This causes an increasing deviation between the host baud rate and the
MCU baud rate. To perform a correct transfer between the MCU and the host without transmission
errors, the deviation Fb of the host baud rate to the MCU baud rate may not exceed 2.5%.
Between Bd
loader. Above Bd
Table 10-2 shows the guaranteed range of baud rates Bd
baud rates above Bd
Table 10-2
Typical Baudrate Selections
MCU clock rate
fosc
8 MHz
12 MHz
16 MHz
Semiconductor Group
min
and Bd
max
Minimum baud rate
Bd
250 baud
370 baud
490 baud
max
only discreet baud rates with a deviation of less than 2.5 % may be used.
min
max
for some MCU clock rates fosc.
every host baud rate can be synchronized successfully by the bootstrap
min
) results in the possible underflow of SFR S0REL when the value of
max
Fb
) is smaller, because of the decreasing resolution of S0REL and
=
high
Bd
0.025
Bd
high
Maximum baud rate
Bd
6580 baud
9380 baud
12830 baud
min
) can be attained if S0REL is set to its maximum value
10-12
max
=
=
Bd
--------------------------------------
(F
--------------
32768
fosc
----------
fosc
host
32
b
Bd
2,5%)
–
host
Bd
min
MCU
to Bd
Functional higher baud
rates
9600, 19200 baud
9600, 19200 baud
19200, 38400 baud
max
and typical functional host
Bootstrap Loader
1997-10-01
C509-L