XR16C864IQ-F Datasheet, PDF (20/51 Pages) Exar Corporation – 2.97V TO 5.5V QUAD UART WITH 128-BYTE FIFO

XR16C864
2.97V TO 5.5V QUAD UART WITH 128-BYTE FIFO
REV. 2.2.0
2.19 Auto RS485 Half-duplex Control
The auto RS485 half-duplex direction control changes the behavior of the transmitter when enabled by FCTR
bit-3. By default, it de-asserts OP1#/RS485 (logic 1) output following the last stop bit of the last character that
has been transmitted. This helps in turning around the transceiver to receive the remote station’s response.
When the host is ready to transmit next polling data packet again, it only has to load data bytes to the transmit
FIFO. The transmitter automatically re-asserts OP1#/RS485 (logic 0) output prior to sending the data.
2.20 Infrared Mode
The 864 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 11 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, 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 11.
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 864 has a provision to invert
the input polarity to accomodate this. In this case, user can enable FCTR bit-2 to invert the input signal.
FIGURE 11. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING
C h a ra cte r
Data Bits
TX Data ^{0 1 0 1 0 0 1 1 0 1}
Transm it
IR Pulse
(TX Pin)
Bit Tim e
3/16 Bit Tim e
1/2 Bit Tim e
IrEncoder-1
Receive
IR Pulse
(RX pin)
RX Data
Bit Time
1/16 Clock Delay
0 1 0 1 0 0 11 0 1
Data Bits
Character
IRdecoder-1
20