Preamble
(16x)
Start Flag
Frame Data
CRC - 32
Stop Flag
Serial Infrared
Interaction Pulse
1.6 us
8.7 us
42x
41x
42x
Baud Adjustment Cyclic Pattern (3 MIR Periods)
Jitter
Jitter
10x
42x
41x
42x
IRTX
Ideal Edge
Placement
IRRX (Inverter
Enabled)
Sampling
Window
Functional Description
Figure 19-21. MIR BAUD Rate Adjustment Mechanism
19.3.8.2.2.2 SIP Generation
In MIR and FIR operation modes, the transmitter needs to send a serial infrared interaction pulse (SIP) at
least once every 500 ms. The purpose of the SIP is to let slow devices (operating in SIR mode) know that
the medium is currently occupied. The SIP pulse is shown in
Figure 19-22. SIP Pulse
When the SIPMODE bit of Mode Definition Register 1 (MDR1[6]) equals 1, the TX state machine will
always send one SIP at the end of a transmission frame. But when MDR1[6] = 0, the transmission of the
SIP depends on the SENDSIP bit of the Auxiliary Control Register (ACREG[3]). The system (LH) can set
ACREG[3] at least once every 500ms. The advantage of this approach over the default approach is that
the TX state machine does not need to send the SIP at the end of each frame which may reduce the
overhead required
19.3.8.2.3 FIR Mode
In fast infrared mode (FIR), data transfers take place between LH and peripheral devices at 4 Mbits/s
speed. A FIR transmit frame starts with a preamble, followed by a start flag, frame data, CRC-32, and
ends with a stop flag.
Figure 19-23. FIR Transmit Frame Format
On transmit, the FIR transmit state machine attaches the preamble, start flag, CRC-32, and stop flag. It
also encodes the transmit data into 4PPM format. It also generates the serial infrared interaction pulse
(SIP).
3484
Universal Asynchronous Receiver/Transmitter (UART)
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated