Description of Operation
13-14
ADSP-BF537 Blackfin Processor Hardware Reference
detection is performed to prevent the UART from starting reception with
incorrect bit rate matching. Alternatively, the UART can be disconnected
from the
RX
pin by setting the
LOOP
bit.
A software routine can detect the pulse widths of serial stream bit cells.
Because the sample base of the timers is synchronous with the UART
operation—all derived from
SCLK
—the pulse widths can be used to calcu-
late the baud rate divider for the UART.
DIVISOR = (TIMERx_WIDTH) / (16 x Number of captured UART bits)
In order to increase the number of timer counts and therefore the resolu-
tion of the captured signal, it is recommended not to measure just the
pulse width of a single bit, but to enlarge the pulse of interest over more
bits. Traditionally, a NULL character (ASCII 0x00) was used in autobaud
detection, as shown in
.
Because the example frame in
encloses 8 data bits and 1 start
bit, apply the formula:
DIVISOR = TIMERx_WIDTH/(16 x 9)
Real UART RX signals often have asymmetrical falling and rising edges,
and the sampling logic level is not exactly in the middle of the signal volt-
age range. At higher bit rates, such pulse width-based autobaud detection
might not return adequate results without additional analog signal condi-
tioning. Measuring signal periods works around this issue and is strongly
recommended.
Figure 13-5. Autobaud Detection Character 0x00
FRAME WIDTH
S
1
2
3
4
5
6
7
STOP
0
Summary of Contents for Blackfin ADSP-BF537
Page 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Page 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...