SAB80515 Datasheet, PDF (51/270 Pages) Siemens Semiconductor Group – 8-Bit Single-Chip Microcontroller Family

On-Chip Peripheral Components
Mode 0
The baud rate in mode 0 is fixed:
Mode 0 baud rate = ^{oscillator frequency}
12
Mode 2
The baud rate in mode 2 depends on the value of bit SMOD in special function register PCON (see
figure 7-9). If SMOD = 0 (which is the value after reset), the baud rate is 1/64 of the oscillator
frequency. If SMOD = 1, the baud rate is 1/32 of the oscillator frequency.
2^SMOD
Mode 2 baud rate =
x oscillator frequency
64
Figure 7-9
Special Function Register PCON (Address 87H)
87H SMOD PDS IDLS
–
GF1 GF0 PDE IDLE PCON
These bits are not used in controlling serial interface.
Bit
SMOD
Function
When set, the baud rate of serial interface in modes 1, 2, 3 is doubled.
Modes 1 and 3
In these modes the baud rate is variable and can be generated alternatively by a dedicated baud
rate generator or by timer 1.
Using the baud rate generator:
In modes 1 and 3, the SAB 80(C)515 can use the internal baud rate generator for the serial
interface. To enable this feature, bit BD (bit 7 of special function register ADCON) must be set (see
figure 7-10). This baud rate generator divides the oscillator frequency by 2500. Bit SMOD
(PCON.7) also can be used to enable a multiply by two prescaler (see figure 7-9). At 12-MHz
oscillator frequency, the commonly used baud rates 4800 baud (SMOD = 0) and 9600 baud (SMOD
= 1) are available. The baud rate is determined by SMOD and the oscillator frequency as follows:
2^SMOD
Mode 1, 3 baud rate =
x oscillator frequency
2500
Semiconductor Group
51