Datasheet

14 - SERIAL CHANNELS ST10F269
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Baud Rate Generation
The Baud rate generator is clocked by f
CPU
/2. The
timer is counting downwards and can be started
or stopped through the global enable bit SSCEN
in register SSCCON. Register SSCBR is the
dual-function Baud Rate Generator/Reload
register. Reading SSCBR, while the SSC is
enabled, returns the content of the timer. Reading
SSCBR, while the SSC is disabled, returns the
programmed reload value. In this mode the
desired reload value can be written to SSCBR.
Note Never write to SSCBR, while the SSC is
enabled.
The formulas below calculate the resulting Baud
rate for a given reload value and the required
reload value for a given Baud rate:
(SSCBR) represents the content of the reload
register, taken as unsigned 16-bit integer.
Table 32 lists some possible Baud rates against
the required reload values and the resulting bit
times for a 40MHz CPU clock.
Table 33 lists some possible Baud rates against
the required reload values and the resulting bit
times for a 32MHz CPU clock.
.
Table 32 : Synchronous Baud Rate and Reload
Values (PQFP144 devices)
Baud Rate Bit Time Reload Value
Reserved use a
reload value > 0.
--- ---
10M Baud 100ns 0001h
5M Baud 200ns 0003h
2.5M Baud 400ns 0007h
1M Baud 1µs 0013h
100K Baud 10µs 00C7h
10K Baud 100µs 07CFh
1K Baud 1ms 4E1Fh
306 Baud 3.26ms FF4Eh
Baud rate
SSC
=
f
CPU
2 x [(SSCBR) + 1]
SSCBR = (
f
CPU
2 x Baud rate
SSC
) - 1
Table 33 : Synchronous Baud Rate and Reload
Values (TQFP144 devices)
Baud Rate Bit Time Reload Value
Reserved use a
reload value > 0.
--- ---
8MBaud 125ns 0001h
4MBaud 250ns 0003h
2MBaud 500ns 0007h
1MBaud 1µs000Fh
500KBaud 2µs001Fh
100KBaud 10µs009Fh
10KBaud 100µs030Ch
1K Baud 1ms 3E7Fh
244.14 Baud 5.24ms FFFFh