XR17D154 Datasheet, PDF (33/69 Pages) Exar Corporation – UNIVERSAL (3.3V AND 5V) PCI BUS QUAD UART

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REV. 1.2.0
XR17D154
UNIVERSAL (3.3V AND 5V) PCI BUS QUAD UART
5.5 Infrared Mode
Each UART in the D154 includes the infrared encoder and decoder compatible to the IrDA (Infrared Data
Association) version 1.0. The input pin ENIR conveniently activates all 4 UART channels to start up in the
infrared mode. The ENIR pin is sampled when the RST# input is de-asserted. This global control pin enables
the MCR bit-6 function in every UART channel register. After power up or a reset, the software can overwrite
MCR bit-6 if so desired. ENIR and MCR bit-6 also disable its receiver while the transmitter is sending data.
This prevents the echoed data from going to the receiver. The global activation ENIR pin prevents the infrared
emitter from turning on and drawing large amount of current while the system is starting up. When the infrared
feature is enabled, the transmit data outputs, TX[3:0], would idle at logic zero level. Likewise, the RX[3:0]
inputs assume an idle level of logic zero.
The infrared encoder sends out a 3/16 of a bit wide 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 17 below.
The infrared decoder receives the input pulse from the infrared sensing diode on RX pin. Each time it senses a
light pulse, it returns a logic zero to the data bit stream. The RX input signal may be inverted prior delivered to
the input of the decoder via internal register setting. This option supports active low instead of normal active
high pulse from some infrared modules on the market.
FIGURE 17. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING
TX Data
C h a ra c te r
Data Bits
0 1 0 1 0 0 11 0 1
T ra n sm it
IR Pulse
(TX Pin)
Bit Time
3/16 Bit Time
1/2 Bit Time
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
C h a ra cte r
IRdecoder-1
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