C515C_9711 Datasheet, PDF (116/268 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C515C
6.3.3.3 Baud Rate in Mode 1 and 3
In these modes the baud rate is variable and can be generated alternatively by a baud rate
generator or by timer 1.
6.3.3.3.1 Using the Internal Baud Rate Generator
In modes 1 and 3, the C515C can use an internal baud rate generator for the serial port. To enable
this feature, bit BD (bit 7 of special function register ADCON0) must be set. Bit SMOD (PCON.7)
controls a divide-by-2 circuit which affect the input and output clock signal of the baud rate
generator. After reset the divide-by-2 circuit is active and the resulting overflow output clock will be
divided by 2. The input clock of the baud rate generator is f_OSC.
Baud Rate Generator
SRELH .1 .0
SRELL
Input
f _OSC
Clock
10 Bit Timer
Overflow
Note : The switch configuration shows the reset state.
PCON.7
(SMOD)
÷2
0
1
Baud
Rate
Clock
MCS02734
Figure 6-30
Serial Port Input Clock when using the Baud Rate Generator
The baud rate generator consists of a free running upward counting 10-bit timer. On overflow of this
timer (next count step after counter value 3FFH) there is an automatic 10-bit reload from the
registers SRELL and SRELH. The lower 8 bits of the timer are reloaded from SRELL, while the
upper two bits are reloaded from bit 0 and 1 of register SRELH. The baud rate timer is reloaded by
writing to SRELL.
Semiconductor Group
6-53
1997-11-01