XR17C154 Datasheet, PDF (30/62 Pages) Exar Corporation – 5V PCI BUS QUAD UART

XR17C154
5V PCI BUS QUAD UART
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REV. 1.3.0
4.5 Infrared Mode
Each UART in the 154 includes the infrared encoder and decoder compatible to the IrDA (Infrared Data
Association) version 1.0. The input pin ENIR conveniently activates all 8 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 LOW. Likewise, the RX [3:0] inputs assume
an idling condition when it is LOW.
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 15 below.
The infrared decoder receives the input pulse from the infrared sensing diode on RX pin. Each time the
decoder 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 15. 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
30