C517A_99 Datasheet, PDF (139/218 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C517A
6.5.1.4 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 abrevation 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)
Reset Value : 00H
Reset Value : 00H
Bit No.
D8H
MSB
DFH
BD
DEH DDH
CLK ADEX
DCH
BSY
DBH
ADM
DAH
MX2
D9H
MX1
LSB
D8H
MX0
ADCON0
7
6
5
4
3
2
1
0
87H SMOD PDS IDLS SD GF1 GF0 PDE IDLE PCON
The shaded bits are not used in controlling serial interface 0.
Bit
BD
SMOD
Function
Baud rate generator enable
When set, the baud rate of serial interface 0 is derived from a dedicated
programmable 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.
Figure 6-33 shows the configuration for the baud rate generation of serial channel 0.
Semiconductor Group
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