C509-L_97 Datasheet, PDF (166/290 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C509-L
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
Reload value. Upper two bits of the timer reload value.
Reload value. Lower 8 bit of 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 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:
2 ^SMOD x oscillator frequency
Mode 1, 3 baud rate =
64 x (baud rate generator overflow rate) x 2^S0P
Baud rate generator overflow rate = 2¹⁰ – S0REL
with S0REL = S0RELH.1 – 0, S0RELL.7 – 0
At 12-MHz oscillator frequency a baud rate range from about 92 baud up to 375 kbaud is covered.
Semiconductor Group
6-88
1997-10-01