Analog Devices ADSP-BF535 Blackfin, Hardware Reference Manual

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IrDA Support
12-38 ADSP-BF535 Blackfin Processor Hardware Reference
IrDA Receiver Description
The IrDA receiver function is more complex than the transmit function,
The receiver must discriminate the IrDA pulse and reject noise. In
addition, pulse widths of less than 1 UART clock period must be detected
per existing standards. Consequently, both the position of valid data rela-
tive to the UART clock and the pulse duration must be considered.
The filter function enables IrDA sampling from the sixth through the
eleventh 16x clock periods. The window is wider than the transmitted
IrDA pulse to allow for clock frequency discrepancies between the trans-
mitter and receiver. Within this window, the receiver incorporates
minimum pulse duration logic to detect valid data.
The pulse duration is specified by the
IRPD
bits using this formula:
IRPD
= (Desired Pulse Width(sec) *
SLCK
frequency)–2
For example, the Infrared Data Association specifies a receive pulse dura-
tion minimum of 1.41

S at 9.6 Kbits/second. For a
SCLK
frequency of
100 MHz,
IRPD
should contain a value of 0x8b. In this example, receive
data during the sampling window, whose duration is greater than 141
SCLK
cycles, is treated as valid data. Figure 12-30 shows the receiver
functionality.