LSI Logic Confidential
15-4
Serial I/O Port
Copyright © 2001, 2002 by LSI Logic Corporation. All rights reserved.
and used to generate the next pulse. This bit is automatically cleared
after the registers and should be reset by the host during the IR transmit
interrupt handling routine if any further bits are to be sent. The IR
transmit interrupt executes immediately after the Pulse Shape Registers
have been loaded, requiring an interrupt latency of one pulse time from
the host.
15.1.2 IR Receive Functionality
The IR interface block is responsible for interrupting the processor on the
receipt of pulses on the SIO_IRRX pin. The IR receive functionality
consists of measuring the period and duty cycle of demodulated
incoming pulses and generating a processor interrupt for the IR software.
The signal period is measured by counting the number of ticks between
falling edges of the input signal; the duty cycle is determined by counting
the number of ticks during which the incoming signal is high. Note that
the tick value is programmable from 1 to 32768 sysclk periods via the
IR_RTP register.
Some protocols, such as the NEC protocol, allow for optimized
processing of noisy inputs by prepending a start pulse of defined length
to all valid transmissions. Other protocols, such as Philips, do not. The
IR interface provides the IR_RFR register for detecting valid start pulse
lengths between 16 and 240 ticks. Filtering is enabled via the IR_RTC
register and is automatically disabled upon receipt of a valid start pulse,
so that the pulses that follow are properly processed.
The IR receive interrupt executes after the tick count value has been
loaded into the Tick Count register (IR_RTC) on each falling edge of the
SIO_IRRX signal. Again, this provides a minimum of 1.125 ms between
interrupts for the NCR protocol (shown in
) and 1.778 ms for
the RC-5 protocol (shown in
).
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