4
Encoding Scheme
16 CYCLES
16 CYCLES
16 CYCLES
16 CYCLES
16XCLK
TXD
IRTXD
7 CS
3 CS
The encoding scheme relies on a
clock being present, which is set
to 16 times the data transmission
baud rate (16XCLX). The encoder
sends a pulse for every space or
“0” that is sent on the TXD line.
On a high to low transition of the
TXD line, the generation of the
pulse is delayed for 7 clock cycles
of the 16XCLK before the pulse is
set high for 3 clock cycles (or
3/16th of a bit time) and then
subsequently pulled low. This
generates a 3/16th bit time pulse
centered around the bit of
information (“0”) that is being
transmitted.
For consecutive spaces, pulses
with a 1 bit time delay are gener-
ated in series. If a logic 1 (mark)
is sent then the encoder does not
generate a pulse.
Decoding Scheme
16 CYCLES
16 CYCLES
16 CYCLES
16 CYCLES
16XCLK
IRRXD
3 CS
RXD
The IrDA-SIR (Serial InfraRed)
decoding modulation method can
be thought of as a pulse stretch-
ing scheme.
Every high to low transition of
the IR_RXD line signifies the
arrival of a pulse. This pulse
needs to be stretched to
accommodate 1 bit time (or 16
16XCLK cycles). Every pulse that
is received is translated into a “0”
or space on the RXD line equal to
1 bit time.
Note 1: The stretched pulse must
be at least 3/4 of a bit time in
duration to be correctly inter-
preted by a UART.
Note 2: It is recommended that
TXD remains high when not
transmitting. This ensures the
LED is off and will not interfere
with signal reception.
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