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Table 4.1
Frame Coding Method
Speed (in bps)
IrDA Speeds and
2400 Chapter 4 / Infrared Communications Overview
SIR
9600 SIR Corresponding
19,200 SIR Frame Coding
Methods
38,400 SIR
57,600 SIR
115,200 SIR
576,000 MIR
1.152 Mb/s MIR
4 Mb/s FIR
16 Mb/s VFIR

Communication Link Turnaround Times
An IR adapter consists of an IR transceiver, along with supporting
hardware for encoding and decoding frames. This IR transceiver con-
tains a transmitter light-emitting diode (LED) and a receiver diode that
are typically located quite close together. The receiver diode is sensi-
tive to IR light because it must receive transmissions from a remote IR
LED over distances up to at least 1 m. The transmitter LED is quite
powerful because it must transmit to a remote receiver diode over the
same distances.
During transmission, a local LED typically emits enough light to satu-
rate the local receiver diode. In much the same way that it is difficult
for people to see well after staring at the sun, it is difficult for the local
receiver diode to correctly receive incoming frames immediately after
the local LED transmits outgoing frames.
To allow time for the local receiver diode to recover from the satura-
tion state and become capable of again receiving incoming frames, the
IrDA protocol defines a parameter known as turnaround time.
Turnaround time specifies the amount of time, in milliseconds, that it
takes the receiver diode to recover from saturation. In some IrDA
devices, the turnaround time may be negligible; in other IrDA devices,
it can be a relatively long period of time.

The turnaround time of the local receiver diode does not affect the
behavior of the local transceiver. However, the turnaround time of the
local receiver diode affects the anticipated behavior of the remote
transceiver. For example, if a local transceiver requires a 1-ms delay

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