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Using automatic baud-rate detection – Texas Instruments TMS320C2XX User Manual

Page 412

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Controlling and Resetting the Port

10-14

Table 10–2. Common Baud Rates and the Corresponding BRD Values

BRD Value in Hexadecimal

Baud
Rate

CLKOUT1 = 20 MHz

(50 ns)

CLKOUT1 = 28.57 MHz

(35 ns)

CLKOUT1 = 40 MHz

(25 ns)

1200

0411

05CC

0823

2400

0208

02E6

0411

4800

0104

0173

0208

9600

0082

00B9

0104

19200

0041

005C

0082

10.3.4 Using Automatic Baud-Rate Detection

The ASP contains auto-baud detection logic, which allows the ASP to lock to
the incoming data rate. The following steps explain the sequence by which the
detection logic could be implemented:

1) Enable auto-baud detection by setting the CAD bit in the ASPCR to 1 and

ADC bit in the IOSR to zero.

2) Receive from a host the ASCII character

A or a as the first character, at

any desired baud rate definable in the BRD register. If the first character
received is

A or a, the serial port will lock to the incoming baud rate (the

rate of the host), and the BRD register will be updated to the incoming baud
rate value.

3) Baud-rate detection is indicated by a TXRXINT interrupt (mapped to vec-

tor location 000Ch) if TXRXINT is unmasked in the interrupt mask register
and is globally enabled by the INTM bit of status register ST0. This inter-
rupt occurs regardless of the values of the DIM, TIM, and RIM bits in the
ASPCR.

4) Following the baud detection interrupt, the ADTR should be read to clear

the

A or a character from the receive buffer. If the ADTR is not cleared, any

subsequent character received will set the OE bit in the IOSR, indicating
an overrun error.

5) Once the baud rate is detected, both the CAD and ADC bits must be

cleared; write 0 to CAD and write 1 to ADC. If CAD is not cleared, the auto
baud-detection logic will try to lock to the incoming character speed. In
addition, for as long as ADC = 1 and CAD = 1, receive interrupts will be
generated.