C509-L_97 Datasheet, PDF (163/290 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C509-L
6.5.1.3 Baud Rates of Serial Channel 0
There are several possibilities to generate the baud rate clock for the serial interface 0 depending
on the mode in which it is operated.
For clarification some terms regarding the difference between “baud rate clock” and “baud rate”
should be mentioned. The serial interface requires a clock rate which is 16 times the baud rate for
internal synchronization. Therefore, the baud rate generators have to provide a “baud rate clock” to
the serial interface which - there divided by 16 - results in the actual “baud rate”. However, all
formulas given in the following section already include the factor and calculate the final baud rate.
Further, the abbreviation f_OSC refers to the oscillator frequency (crystal or external clock operation).
The baud rate of the serial channel 0 is controlled by several bits which are located in the special
function registers as shown below.
Special Function Register ADCON0 (Address D8H)
Special Function Register PCON (Address 87H)
Special Function Register PRSC (Address B4H)
Reset Value : 00H
Reset Value : 00H
Reset Value : 11010101B
Bit No.
D8H
MSB
DFH
BD
DEH DDH DCH DBH DAH D9H
CLK ADEX BSY ADM MX2 MX1
LSB
D8H
MX0
ADCON0
7
6
5
4
3
2
1
0
87H SMOD PDS IDLS SD GF1 GF0 PDE IDLE PCON
7
6
B4H WDTP S0P
5
4
3
2
1
0
T2P1 T2P0 T1P1 T1P2 T0P1 T0P0
PRSC
The shaded bits are not used in controlling serial interface 0.
Bit
BD
SMOD
S0P
Function
Baud rate generator enable
When set, the baud rate of serial interface 0 is derived from a dedicated baud rate
generator. When cleared (default after reset), baud rate is derived from the timer
1 overflow rate.
Double baud rate
When set, the baud rate of serial interface 0 in modes 1, 2, 3 is doubled. After
reset this bit is cleared.
Serial interface 0 prescaler
When set (default after reset), an additional prescaler by 2 is active at the
dedicated baud rate generator.
Semiconductor Group
6-85
1997-10-01