C501G-1E SIEMENS [Siemens Semiconductor Group], C501G-1E Datasheet - Page 66

• Manufacturer Part Number: C501G-1E
• Description: 8-Bit Single-Chip Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

6.3.3 Baud Rates 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
operation).
The baud rate of the serial port is controlled by bit SMOD which is located in the special function
register PCON as shown below.
Special Function Register PCON (Address 87 H )
Bit
SMOD
Mode 0
The baud rate in mode 0 is fixed:
Mode 2
The baud rate in mode 2 depends on the value of bit SMOD in special function register PCON. If
SMOD = 0 (which is the value on reset), the baud rate is
32.
Modes 1 and 3
The baud rates in mode 1 and 3 are determined by the timer overflow rate. These baud rates can
be determined by timer 1 or by timer 2 or by both (one for transmit and the other for receive).
Semiconductor Group
Bit No.
Mode 0 baud rate = oscillator frequency/12 =
Mode 2 baud rate = 2
87 H
SMOD
MSB
Function
Double baud rate
When set, the baud rate of serial interface in modes 1, 2, 3 is doubled. After reset
this bit is cleared.
7
The shaded bits are not used for controlling the baud rate.
f
OSC
–
6
SMOD
refers to the external clock frequency (oscillator or external input clock
/64 (
–
5
f
OSC
)
–
4
6-32
GF1
f
3
OSC
On-Chip Peripheral Components
/12
f
OSC
GF0
2
/64. If SMOD = 1, the baud rate is
PDE
1
Reset Value : 0XXX0000 B
IDLE
LSB
0
PCON
C501
f
OSC
/