Texas Instruments MSP430x4xx Family, User Manual

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USCI Operation: UART Mode
19-12 Universal Serial Communication Interface, UART Mode
19.3.5 IrDA Encoding and Decoding
When UCIREN is set the IrDA encoder and decoder are enabled and provide
hardware bit shaping for IrDA communication.
IrDA Encoding
The encoder sends a pulse for every zero bit in the transmit bit stream coming
from the UART as shown in Figure 19−7. The pulse duration is defined by
UCIRTXPLx bits specifying the number of half clock periods of the clock
selected by UCIRTXCLK.
Figure 19−7. UART vs. IrDA Data Format
UART
Start
Bit
Data Bits
Stop
Bit
IrDA
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.
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.