ST16C650A
2.90V TO 5.5V UART WITH 32-BYTE FIFO
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REV. 5.0.0
2.16 Infrared Mode
The 650A UART includes the infrared encoder and decoder compatible to the IrDA (Infrared Data Association)
version 1.0. The infrared mode can be enabled by setting MCR bit-6 to a ‘1’. In the infrared mode, the user can
choose to send/receive data either half-duplex or full-duplex. The half-duplex mode is chosen by setting bit-0
of XFR register to a ‘1’. This prevents echoed data from reaching the receiver. When the infrared feature is
enabled, the transmit data outputs, TX, idles at logic zero level. Likewise, the RX input assumes an idle level of
logic zero, see Figure 14.
The IrDA standard defines the infrared encoder sends out a 3/16 of a bit wide HIGH-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 14 below. The 650A has an additional feature to allow user to vary the transmit pulse
width further reducing power consumption of the system where application permits (see IRPW register for
details).
The wireless 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 0 to the data bit stream. The 650A also includes another feature -
inversion of the IR pulse (XFR register bit-1), where a LOW IR pulse in the receive data stream is recognized
as a ’0’ bit.
FIGURE 14. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING
Character
Data Bits
1
1
1
1
1
0
0
0
0
0
TX Data
Transm it
IR Pulse
(TX Pin)
1/2 Bit Tim e
Bit Tim e
3/16 Bit Tim e
IrEncoder-1
Receive
IR Pulse
(RX pin)
Bit Time
1/16 Clock Delay
1
1
1
1
1
0
0
0
0
0
RX Data
Data Bits
Character
IRdecoder-1
20
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