42x
41x
42x
Baud adjustment cyclic pattern (3 MIR periods)
uart3_tx_irtx
Jitter
Jitter
10x
uart3_rx_irrx
(inverter enabled)
42x
41x
42x
Sampling
window
Ideal edge
placement
uart-011
Serial infrared
interaction pulse
1.6
m
s
8.7
m
s
108-012
Public Version
UART/IrDA/CIR Environment
www.ti.com
19.2.5.2.3.1 MIR Encoder/Decoder
To meet the MIR baud rate tolerance of +/-0.1 percent with a 48-MHz clock input, a 42-41-42
encoding/decoding adjustment is performed. The reference start point is the first start flag, and the
42-41-42 cyclic pattern is repeated until the stop flag is sent or detected.
The jitter created this way is within MIR tolerances. The pulse width is not exactly 1/4, but it is within the
tolerances defined by the IrDA specifications.
shows the MIR baud rate adjustment mechanism.
Figure 19-11. MIR Baud Rate Adjustment Mechanism
19.2.5.2.3.2 SIP Generation
In the MIR and FIR operation modes, the transmitter must send a serial infrared interaction pulse (SIP) at
least once every 500 ms. The SIP informs slow devices (operating in SIR mode) that the medium is
currently occupied.
shows the SIP.
Figure 19-12. SIP
19.2.5.2.4 FIR Mode
In FIR mode, data is transferred between the MPU and the peripheral devices at 4M bits/s. A FIR transmit
frame starts with a preamble that is followed by a start flag, frame data, CRC-32, and ends with a stop
flag.
shows the FIR transmit frame format.
2880
UART/IrDA/CIR
SWPU177N – December 2009 – Revised November 2010
Copyright © 2009–2010, Texas Instruments Incorporated