XR16C850CM-F Datasheet, PDF (21/56 Pages) Exar Corporation – 2.97V TO 5.5V UART WITH 128-BYTE FIFO

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REV. 2.3.1
XR16C850
2.97V TO 5.5V UART WITH 128-BYTE FIFO
FIGURE 14. AUTO RS-485 HALF-DUPLEX CONTROL
850 UART
RS-485 Transceiver
TX
OP1#/RS485
(0 = Transmit
1= Receive)
RX
T+
D
T-
R+
R
R-
2.20 Infrared Mode
The 850 UART includes the 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 15.
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, TX, idles at logic zero level. Likewise, the RX input assumes an idle level
of logic zero from a reset and power up, see Figure 15.
Typically, the wireless infrared decoder receives the input pulse from the infrared sensing diode on the RX pin.
Each time it senses a light pulse, it returns a logic 1 to the data bit stream. However, this is not true with some
infrared modules on the market which indicate a logic 0 by a light pulse. So the 850 has a provision to invert
the input polarity to accomodate this. In this case, the user can enable FCTR bit-2 to invert the incoming
infrared RX signal.
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