pc87317vul National Semiconductor Corporation, pc87317vul Datasheet - Page 164

• Manufacturer Part Number: pc87317vul
• Description: Pc87317vul/pc97317vul Superi/o Plug And Play Compatible With Acpi Compliant Controller/extender
• Manufacturer: National Semiconductor Corporation

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a 0 value start bit, followed by eight data bits (LSB first), an
optional parity bit, and ending with at least one stop bit with
a binary value of 1.
A zero value is signalled by sending a single infrared pulse.
A one value is signalled by not sending any pulse. The width
of each pulse can be either 1.6 sec or 3/16 of the time re-
quired to transmit a single bit. (1.6 sec equals 3/16 of the
time required to transmit a single bit at 115.2 Kbps). This
way, each word begins with a pulse for the start bit.
The module operation in SIR is similar to the operation in
UART mode, the main difference being that data transfer
operations are normally performed in half duplex fashion.
Selection of the IrDA 1.0 SIR mode is controlled by the
MDSL bits in the MCR register when the UART is in Extend-
ed mode, or by the IR_SL bits in the IRCR1 register when
the UART is not in Extended mode. This prevents legacy
software, running in Non-Extended mode, from spuriously
switching the module to UART mode, when the software
writes to the MCR register.
7.7 CONSUMER-IR MODE – DETAILED DESCRIPTION
The Consumer-IR circuitry in this module is designed to op-
timally support all the major protocols presently used in re-
mote-controlled home entertainment equipment: RC-5, RC-
6, RECS 80, NEC and RCA.
This module, in conjunction with an external optical device,
provides the physical layer functions necessary to support
these protocols. These functions include: modulation, de-
modulation, serialization, deserialization, data buffering,
status reporting, interrupt generation, etc.
The software is responsible for the generation of the infra-
red code to be transmitted, and for the interpretation of the
received code.
7.7.1
The code to be transmitted consists of a sequence of bytes
that represent either a bit string or a set of run-length codes.
The number of bits or run-length codes usually needed to
represent each infrared code bit depends on the infrared
protocol to be used. The RC-5 protocol, for example, needs
two bits or between one and two run-length codes to repre-
sent each infrared code bit.
Transmission is initiated when the CPU or DMA module
writes code bytes into the empty TX_FIFO. Transmission is
normally completed when the CPU sets the S_EOT bit in
the ASCR register (See Section 7.11.10 on page 175), be-
fore writing the last byte, or when the DMA controller acti-
vates the TC (terminal count) signal. Transmission will also
terminate if the CPU simply stops transferring data and the
transmitter becomes empty. In this case, however, a trans-
mitter-underrun condition will be generated, which must be
cleared in order to begin the next transmission.
The transmission bytes are either de-serialized or run-
length encoded, and the resulting bit string modulates a car-
rier signal and is sent to the transmitter LED. The transfer
rate of this bit string, like in the UART mode, is determined
by the value programmed in the Baud Generator Divisor
Registers. Unlike a UART transmission, start, stop and par-
ity bits are not included in the transmitted data stream. A
logic 1 in the bit string keeps the LED off, so no infrared sig-
nal is transmitted. A logic 0, generates a sequence of mod-
ulating pulses which will turn on the transmitter LED.
Frequency and pulse width of the modulating pulses are
programmed by the MCFR and MCPW fields in the
Consumer-IR Transmission
Enhanced Serial Port with IR - UART2 (Logical Device 5)
164
IRTXMC register as well as the TXHSC bit in the RCCFG
register. Sections 7.18.2 and 7.18.3 describe these regis-
ters in detail.
The RC_MMD field selects the transmitter modulation
mode. If C_PLS mode is selected, modulating pulses are
generated continuously for the entire logic 0 bit time. If
6_PLS or 8_PLS mode is selected, six or eight pulses are
generated each time a logic 0 bit is transmitted following a
logic 1 bit. The total transmission time for the logic 0 bits
must be equal-to or greater-than 6 or 8 times the period of
the modulation subcarrier, otherwise, fewer pulses will be
transmitted.
C_PLS modulation mode is used for RC-5, RC-6, NEC and
RCA protocols. 8_PLS or 6_PLS modulation mode is used
for the RECS 80 protocol. The 8_PLS or 6_PLS mode al-
lows minimization of the number of bits needed to represent
the RECS 80 infrared code sequence. The current transmit-
ter implementation supports only the modulated modes of
the RECS 80 protocol. It does not support Flash mode.
7.7.2
The Consumer-IR receiver is significantly different from a
UART receiver in two ways. Firstly, the incoming infrared
signals are DASK modulated. Therefore, demodulation may
be necessary. Secondly, there are no start bits in the incom-
ing data stream.
Whenever an infrared signal is detected, receiver opera-
tions depend on whether or not receiver demodulation is en-
abled. If demodulation is disabled, the receiver immediately
becomes active. If demodulation is enabled, the receiver
checks the carrier frequency of the incoming signal, and be-
comes active only if the frequency is within the programmed
range. Otherwise, the signal is ignored and no other action
is taken.
When the receiver enters the active state, the RXACT bit in
the ASCR register is set to 1. Once in the active state, the
receiver keeps sampling the infrared input signal and gen-
erates a bit string where a logic 1 indicates an idle condition
and a logic 0 indicates the presence of infrared energy. The
infrared input is sampled regardless of the presence of in-
frared pulses at a rate determined by the value loaded into
the Baud Generator Divisor Registers. The received bit
string is either de-serialized and assembled into 8-bit char-
acters, or it is converted to run-length encoded values. The
resulting data bytes are then transferred into the RX_FIFO.
The receiver also sets the RXWDG bit in the ASCR register
each time an infrared pulse signal is detected. This bit is au-
tomatically cleared when the ASCR register is read, and it
is intended to assist the software in determining when the
infrared link has been idle for a certain time. The software
can then stop the data reception by writing a 1 into the RX-
ACT bit to clear it and return the receiver to the inactive
state.
The frequency bandwidth for the incoming modulated infra-
red signal is selected by the DFR and DBW fields in the IR-
RXDC register.
There are two Consumer-IR reception data modes: “Over-
sampled” and “Programmed T Period” mode. For either
mode the sampling rate is determined by the setting of the
Baud Generator Divisor Registers.
The “Over-sampled” mode can be used with the receiver
demodulator either enabled or disabled. It should be used
with the demodulator disabled when a detailed snapshot of
the incoming signal is needed, for example to determine the
period of the carrier signal. If the demodulator is enabled,
Consumer-IR Reception