XR19L402 Datasheet, PDF (19/50 Pages) Exar Corporation – TWO CHANNEL INTEGRATED UART AND RS-485 TRANSCEIVER

XR19L402
REV. 1.0.0
TWO CHANNEL INTEGRATED UART AND RS-485 TRANSCEIVER
2.15 Infrared Mode (UART Channel B Only)
The L402 includes an infrared encoder and decoder compatible to the IrDA (Infrared Data Association) version
1.0. The IrDA 1.0 standard that stipulates the infrared encoder sends out a 3/16 of a bit wide HIGH-pulse for
each “0” bit in the transmit data stream. This signal encoding reduces the on-time of the infrared LED, hence
reduces the power consumption. See Figure 10 below.
The infrared encoder and decoder are enabled by setting MCR register bit-6 to a ‘1’. When the infrared feature
is enabled, the transmit data output, TXB, idles at logic zero level. Likewise, the RX input assumes an idle level
of logic zero from a reset and power up, see Figure 10.
Typically, the wireless infrared decoder receives the input pulse from the infrared sensing diode on the RXB
pin. Each time it senses a light pulse, it returns a HIGH to the data bit stream. However, this is not true with
some infrared modules on the market which indicate a LOW by a light pulse. So the L402 has a provision to
invert the input polarity to accommodate this. In this case user can enable FCTR bit-2 to invert the input signal.
The Infrared Mode can only be used with channel B of the L402 using the TXB output and the RXB input pins.
FIGURE 10. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING
Character
Data Bits
TX Data ^{0 1 0 1 0 0 1 1 0 1}
Transmit
IR Pulse
(TX Pin)
Receive
IR Pulse
(RX pin)
Bit Time
3/16 Bit Time
Bit Time
1/16 Clock Delay
1/2 Bit Time
IrEncoder-1
RX Data
0 1 0 1 0 0 11 0 1
Data Bits
Character
IRdecoder-
19