C515A_9708 Datasheet, PDF (96/182 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C515A
Figure 6-23
Baud Rate Generation for the Serial Port
Depending on the programmed operating mode different paths are selected for the baud rate clock
generation. Table 6-5 shows the dependencies of the serial port baud rate clock generation from
the 3 control bits and from the mode which is selected in the special function register SCON.
Table 6-5
Serial Interface 0 - Baud Rate Dependencies
Serial Interface 0
Operating Modes
Mode 0 (Shift Register)
Mode 1 (8-bit UART)
Mode 3 (9-bit UART)
Mode 2 (9-bit UART)
Active Control Bits Baud Rate Clock Generation
BD
SMOD
–
–
Fixed baud rate clock fosc/12
X
X
BD=0 : Timer 1 overflow is used for baud rate
generation; SMOD controls a divide-by-
2 option.
BD=1 : Baud rate generator is used for baud
rate generation; SMOD controls a
divide-by-2 option .
–
X
Fixed baud rate clock fosc/32 (SMOD=1) or
fosc/64 (SMOD=0)
Semiconductor Group
6-45
1997-08-01