PC87309 Datasheet, PDF (105/192 Pages) National Semiconductor (TI) – PC87309 SuperI/O Plug and Play Compatible Chip in Compact 100-Pin VLJ Packaging

Enhanced Serial Port with IR -UART2 (Logical Device 2)
5.5 SHARP-IR MODE – DETAILED DESCRIPTION
This mode supports bidirectional data communication with
a remote device using infrared radiation as the transmission
medium. Sharp-IR uses Digital Amplitude Shift Keying
(DASK) and allows serial communication at baud rates up
to 38.4 Kbaud. The format of the serial data is similar to the
UART data format. Each data word is sent serially begin-
ning with a zero value start bit, followed by up to eight data
bits (LSB first), an optional parity bit, and ending with at
least one stop bit with a binary value of one. A logical zero
is signalled by sending a 500 KHz continuous pulse train of
infrared radiation. A logical 1 is signalled by the absence of
any infrared signal. This module can perform the modula-
tion and demodulation operations internally, or can rely on
the external optical module to perform them.
Sharp-IR device operation is similar to the operation in
UART mode, the main difference being that data transfer
operations are normally performed in half duplex fashion,
and the modem control and status signals are not used. Se-
lection of the Sharp-IR mode is controlled by the Mode Se-
lect (MDSL) bits in the MCR register when the module is in
Extended mode, or by the IR_SL bits in the IRCR1 register
when the module is not in extended mode. This prevents
legacy software, running in non-extended mode, from spu-
riously switching the module to UART mode, when the soft-
ware writes to the MCR register.
5.6 SIR MODE – DETAILED DESCRIPTION
This operational mode supports bidirectional data commu-
nication with a remote device using infrared radiation as the
transmission medium.
SIR allows serial communication at baud rates up to
115.2 Kbuad. The serial data format is similar to the UART
data format. Each data word is sent serially beginning with
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 µsec or 3/16 of the time re-
quired to transmit a single bit. (1.6 µsec 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.
5.7 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.
5.7.1 Consumer-IR Transmission
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 5.11.10 on page 117), 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
IRTXMC register as well as the TXHSC bit in the RCCFG
register. Sections 5.18.2 and 5.18.3 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.
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