XR20M1172G28-0B Datasheet, PDF (22/55 Pages) Exar Corporation – TWO CHANNEL I2C/SPI UART WITH 64-BYTE FIFO

XR20M1172
TWO CHANNEL I2C/SPI UART WITH 64-BYTE FIFO
REV. 1.2.0
2.15 Infrared Mode
The M1172 UART includes the infrared encoder and decoder compatible to the IrDA (Infrared Data
Association) version 1.0 and 1.1. The IrDA 1.0 standard that stipulates the infrared encoder sends out a 3/16 of
a bit wide HIGH-pulse for each “0” bit in the transmit data stream with a data rate up to 115.2 Kbps. For the
IrDA 1.1 standard, the infrared encoder sends out a 1/4 of a bit time wide HIGH-pulse for each "0" bit in the
transmit data stream with a data rate up to 1.152 Mbps. This signal encoding reduces the on-time of the
infrared LED, hence reduces the power consumption. See Figure 18 below.
The infrared encoder and decoder are enabled by setting MCR register bit-6 to a ‘1’. With this bit enabled, the
infrared encoder and decoder is compatible to the IrDA 1.0 standard. For the infrared encoder and decoder to
be compatible to the IrDA 1.1 standard, EFCR bit-7 will also need to be set to a ’1’. When the infrared feature
is enabled, the transmit data output, TX, idles LOW. Likewise, the RX input also idles LOW, see Figure 18.
The wireless infrared decoder receives the input pulse from the infrared sensing diode on the RX pin. Each
time it senses a light pulse, it returns a logic 1 to the data bit stream.
The UART can be in the infrared mode upon power-up if the ENIR# pin is LOW. After power-up, the infrared
mode can be controlled via MCR bit-6.
FIGURE 18. 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)
Receive
IR Pulse
(RX pin)
Bit Time
3/16 or 1/4
Bit Time
Bit Time
1/16 Clock Delay
1/2 Bit Time
IrEncoder-1
RX Data
0 1 0 1 0 0 11 0 1
Data Bits
Character
IRdecoder-1
22