Analog Devices ADSP-BF535 Blackfin, Hardware Reference Manual

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Timer Modes
16-20 ADSP-BF535 Blackfin Processor Hardware Reference
Use the equation above if you are capturing either the pulse width of a sin-
gle bit or the duration of a NULL-character frame, as shown in
Figure 16-11 .
Because the example frame in Figure 16-11 encloses 8 data bits and 1 start
bit, apply the formula:
DIVISOR = TIMERx_WIDTH/(16

9)
At higher bit rates such pulse-width-based autobaud detection might not
return sufficient results without additional analog signal conditioning.
Therefore, it is strongly recommended to measure signal periods instead.
For example, predefine ASCII character “@” (40h) as an autobaud detec-
tion byte and measure the period between the falling edge of the start bit
and the falling edge after bit 6, as shown in
Figure 16-12 . Since this
period enclosed 8 bits, apply the formula:
DIVISOR = TIMERx_PERIOD/(16

8)
Figure 16-11. Autobaud Detection Character 0x00
Figure 16-12. Autobaud Detection Character 0x40
Fr am e Wi d th
S 0 1 2 3 4 5 6 7 STO P
P er io d
S 0 1 2 3 4 5 6 7 STO P