XR17V254_08 Datasheet, PDF (33/70 Pages) Exar Corporation – 66MHZ PCI BUS QUAD UART WITH POWER MANAGEMENT SUPPORT

XR17V254
REV. 1.0.1
66MHZ PCI BUS QUAD UART WITH POWER MANAGEMENT SUPPORT
4.3 Infrared Mode
Each UART in the V254 includes the infrared encoder and decoder compatible to the IrDA (Infrared Data
Association) version 1.0. The input pin ENIR conveniently activates all 4254 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[7:0], would
idle at logic 0 level. Likewise, the RX [7:0] inputs assume an idle level of logic 0.
The infrared encoder sends out a 3/16 of a bit wide pulse for each “LOW” bit in the transmit data stream. This
signal encoding reduces the on-time of the infrared LED, hence reduces the power consumption. See
Figure 13 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 LOW 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 13. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING
Character
Data Bits
TX Data ^{0 1 0 1 0 0 1 1 0 1}
Transmit
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
Character
IRdecoder-
33