Datasheet

UART
Start
Bit
Data Bits
Stop
Bit
IrDA
www.ti.com USCI Operation: UART Mode
15.3.4.1 Transmitting a Break/Synch Field
The following procedure transmits a break/synch field:
• Set UCTXBRK with UMODEx = 11.
• Write 055h to UCAxTXBUF. UCAxTXBUF must be ready for new data (UCAxTXIFG = 1).
This generates a break field of 13 bits followed by a break delimiter and the synch character. The
length of the break delimiter is controlled with the UCDELIMx bits. UCTXBRK is reset automatically
when the synch character is transferred from UCAxTXBUF into the shift register.
• Write desired data characters to UCAxTXBUF. UCAxTXBUF must be ready for new data
(UCAxTXIFG = 1).
The data written to UCAxTXBUF is transferred to the shift register and transmitted as soon as the shift
register is ready for new data.
15.3.5 IrDA Encoding and Decoding
When UCIREN is set the IrDA encoder and decoder are enabled and provide hardware bit shaping for
IrDA communication.
15.3.5.1 IrDA Encoding
The encoder sends a pulse for every zero bit in the transmit bit stream coming from the UART as shown
in Figure 15-7. The pulse duration is defined by UCIRTXPLx bits specifying the number of half clock
periods of the clock selected by UCIRTXCLK.
Figure 15-7. UART vs IrDA Data Format
To set the pulse time of 3/16 bit period required by the IrDA standard the BITCLK16 clock is selected with
UCIRTXCLK = 1 and the pulse length is set to 6 half clock cycles with UCIRTXPLx = 6 – 1 = 5.
When UCIRTXCLK = 0, the pulse length t
PULSE
is based on BRCLK and is calculated as follows:
UCIRTXPLx = t
PULSE
× 2 × f
BRCLK
− 1
When the pulse length is based on BRCLK the prescaler UCBRx must to be set to a value greater or
equal to 5.
15.3.5.2 IrDA Decoding
The decoder detects high pulses when UCIRRXPL = 0. Otherwise it detects low pulses. In addition to the
analog deglitch filter an additional programmable digital filter stage can be enabled by setting UCIRRXFE.
When UCIRRXFE is set, only pulses longer than the programmed filter length are passed. Shorter pulses
are discarded. The equation to program the filter length UCIRRXFLx is:
UCIRRXFLx = (t
PULSE
− t
WAKE
) × 2 × f
BRCLK
− 4
Where,
t
PULSE
= Minimum receive pulse width
t
WAKE
= Wake time from any low power mode. Zero when MSP430 is in active mode.
417
SLAU144J–December 2004–Revised July 2013 Universal Serial Communication Interface, UART Mode
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