16XCLK
RXD
RX Output Of
Transceiver
RX Input
(MDR2[6]=1)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Functional Description
19.3.8.2.1.6 Decoder
After reset, RXD is high and the 4-bit counter is cleared. When a rising edge is detected on RX, RXD falls
on the next rising edge of 16XCLK with sufficient setup time. RXD stays low for 16 cycles (16XCLK) and
then returns to high as required by the IrDA specification. As long as no pulses (rising edges) are detected
on the RX, RXD remains high.
Figure 19-18. IrDA Decoding Mechanism
The operation of the RX input can be disabled with DISIRRX bit of the Auxiliary Control Register
(ACREG[5]). Furthermore, the MDR2[6] can be used to invert the signal from the transceiver (RX ouput)
pin to the IRRX logic inside the UART.
19.3.8.2.1.7 IR Address Checking
In all IR modes, if address checking has been enabled, only frames intended for the device are written to
the RX FIFO. This is to avoid receiving frames not meant for this device in a multi-point infrared
environment. It is possible to program two frame addresses that the UART IrDA receives with
XON1/ADDR1 and XON2/ADDR2 registers. Selecting address1 checking is done by setting EFR[0] to 1;
address2 checking is done by setting EFR[1] to 1.
Setting EFR[1:0] to 0 disables all address checking operations. If both bits are set, then the incoming
frame is checked for both private and public addresses. If address checking is disabled, then all received
frames are written into the reception FIFO.
19.3.8.2.1.8 SIR Free Format Mode
To allow complete software flexibility in the transmission and reception of Infrared data packets, the SIR
free format mode is a sub-function of the existing SIR mode such that all frames going to and from the
FIFO buffers are untouched with respect to appending and removing control characters and CRC values.
In the transmission phase, the mode uses the IRTX pin, as in SIR mode.
This mode corresponds to a UART mode with a pulse modulation of 3/16 of baud-rate pulse width.
For example, a normal SIR packet has BOF control and CRC error checking data appended (transmitting)
or removed (receiving) from the data going to and from the FIFOs. In SIR free format mode, only the data
termed the FIFO DATA area, illustrated in
, would be transmitted and received.
3482
Universal Asynchronous Receiver/Transmitter (UART)
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated