C517A_99 Datasheet, PDF (142/218 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C517A
The baud rate generator consists of a free running upward counting 10-bit timer. On overflow of this
timer (next count step after counter value 3FFH) there is an automatic 10-bit reload from the
registers S0RELL and S0RELH. The lower 8 bits of the timer are reloaded from S0RELL, while the
upper two bits are reloaded from bit 0 and 1 of register S0RELH. The baud rate timer is reloaded
by writing to S0RELL.
Special Function Register S0RELH (Address BAH)
Special Function Register S0RELL (Address AAH)
Reset Value : XXXXXX11B
Reset Value : D9H
Bit No. MSB
LSB
7
6
5
4
3
2
1
0
BAH
–
–
–
–
–
– MSB .0
S0RELH
7
6
5
4
3
2
1
0
AAH .7
.6
.5
.4
.3
.2
.1 LSB S0RELL
Bit
S0RELH.0-1
S0RELL.0-7
Function
Baudrate generator for serial interface 0 reload high value
Upper two bits of the baudrate timer reload value.
Baudrate generator for serial interface 0 reload low value
Lower 8 bits of the baudrate timer reload value.
After reset S0RELH and S0RELL have a reload value of 3D9H. With this reload value the baud rate
generator has an overflow rate of input clock/39. With this reset value and a 12-MHz oscillator
frequency, the commonly used baud rates 4800 baud (SMOD = 0) and 9600 baud (SMOD = 1) are
available (with 0.16 % deviation).
With the baud rate generator as clock source for the serial port 0 in mode 1 and 3, the baud rate of
can be determined as follows:
Mode 1, 3 baud rate =
2^SMOD x oscillator frequency
64 x (baud rate generator overflow rate)
Baud rate generator overflow rate = 2¹⁰ – S0REL
with S0REL = S0RELH.1 – 0, S0RELL.7 – 0
Semiconductor Group
6-76