Irda Receive Operation - Analog Devices ADSP-BF506F Hardware Reference Manual

Description of Operation

IrDA Receive Operation

The IrDA receiver function is more complex than the transmit function.
The receiver must discriminate the IrDA pulse and reject noise. To do
this, the receiver looks for the IrDA pulse in a narrow window centered
around the middle of the expected pulse.
Glitch filtering is accomplished by counting 16 system clocks from the
time an initial pulse is seen. If the pulse is absent when the counter
expires, it is considered a glitch. Otherwise, it is interpreted as a 0. This is
acceptable because glitches originating from on-chip capacitive cross-cou-
pling typically do not last for more than a fraction of the system clock
period. Sources outside of the chip and not part of the transmitter can be
avoided by appropriate shielding. The only other source of a glitch is the
transmitter itself. The processor relies on the transmitter to perform
within specification. If the transmitter violates the specification, unpre-
dictable results may occur. The 4-bit counter adds an extra level of
protection at a minimal cost. Note because the system clock can change
across systems, the longest glitch tolerated is inversely proportional to the
system clock frequency.
The receive sampling window is determined by a counter that is clocked at
the 16x bit-time sample clock. The sampling window is re-synchronized
with each start bit by centering the sampling window around the start bit.
15-14 ADSP-BF50x Blackfin Processor Hardware Reference