C505_9708 SIEMENS [Siemens Semiconductor Group], C505_9708 Datasheet - Page 108

• Manufacturer Part Number: C505_9708
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

6.3.3 Baud Rate Generation
There are several possibilities to generate the baud rate clock for the serial port depending on the
mode in which it is operating.
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
operation).
The baud rate of the serial port is controlled by two bits which are located in the special function
registers as shown below.
Special Function Register ADCON0 (Address D8 H )
Special Function Register PCON (Address 87 H )
Bit
BD
SMOD
–
Figure 6-22 shows the configuration for the baud rate generation of the serial port.
Semiconductor Group
Bit No.
D8 H
87 H
SMOD
MSB
DF H
BD
Function
Baud rate generator enable
When set, the baud rate of serial interface is derived from the 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 in modes 1, 2, 3 is doubled. After reset
this bit is cleared.
Reserved bits for future use. Read by CPU returns undefined values.
7
The shaded bits are not used for controlling the baud rate.
PDS
OSC
CLK
DE H
6
refers to the external clock frequency (oscillator or external input clock
IDLS
DD H
–
5
BSY
DC H
SD
4
6-46
ADM
GF1
DB H
3
On-Chip Peripheral Components
GF0
MX2
DA H
2
PDE
MX1
D9 H
1
Reset Value : 00X00000 B
IDLE
LSB
MX0
D8 H
0
Reset Value : 00 H
C505 / C505C
PCON
ADCON0
1997-08-01