XR17L152 Datasheet, PDF (24/55 Pages) Exar Corporation – 3.3V PCI BUS DUAL UART

áç
DISCONTINUED
XR17L152
3.3V PCI BUS DUAL UART
REV. 1.1.0
4.3 Infrared Mode
Each UART in the L152 includes the infrared encoder and decoder compatible to the IrDA (Infrared Data
Association) version 1.0. The input pin ENIR conveniently activates both UART channels to start up in the
infrared mode. 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[1:0], would
idle at logic zero level. Likewise, the RX[1:0] 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 10 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. This option supports active low instead of normal active high pulse from some infrared
modules on the market.
FIGURE 10. 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 c te r
IRdecoder-1
24