XR17D154 Exar Corporation, XR17D154 Datasheet - Page 27

• Manufacturer Part Number: XR17D154
• Description: Four-channel Pci-bus Uart
• Manufacturer: Exar Corporation

XR17D154
UNIVERSAL (3.3V AND 5V) PCI BUS QUAD UART
REV. P1.0.0
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. 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 12
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.
5.3
Infrared Mode
below.
F
IGURE
Receive
IR Pulse
(RX pin)
RX Data
TX Data
Transmit
IR Pulse
(TX Pin)
12. I
NFRARED
0
Bit Time
1
T
RANSMIT
Bit Time
0
0
1/16 Clock Delay
1
1
D
Character
Data Bits
ATA
0
0
3/16 Bit Time
E
NCODING AND
1
0
27
Data Bits
Character
1
0
1
0
0
R
ECEIVE
1
1
1/2 Bit Time
1
IrEncoder-1
D
ATA
0
D
ECODING
1
IRdecoder-1
PRELIMINARY
áç
áç
áç
áç