PC97338VLJ datasheet(147/221 Pages) NSC

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The UART mode is the default mode of operation af-

ter power up or reset. In fact, after reset, the module

enters the 16450 compatibility mode. In addition to

the 16450 and 16550 compatibility modes, an extend-

ed mode of operation is also available. When the ex-

tended mode is selected, the module architecture

changes slightly and a variety of additional features

are made available. The interrupt sources are no

longer prioritized, and an auxiliary status and control

tional features include: transmitter FIFO thresholding,

DMA capability, and interrupts on transmitter empty

and DMA event.

The clock for both transmit and receive channels is

provided by an internal baud generator that divides its

input clock by any divisor value from 1 to 2

16 –1. The

output clock frequency of the baud generator must be

programmed to be sixteen times the baud rate value.

The baud generator input clock is derived from a 24

MHz clock through a programmable prescaler. The

prescaler value is determined by the PRESL bits in

the EXCR2 register. Its default value is 13. This al-

lows all the standard baud rates, up to 115.2 kbaud to

be obtained. Smaller prescaler values will allow baud

rates up to 921.6 kbaud (standard) and 1.5 Mbaud

(non standard).

Before operation can begin, both the communications

format and baud rate must be programmed by the

software. The communications format is programmed

by loading a control byte into the LCR register, while

the baud rate is selected by loading an appropriate

value into the baud generator divisor register. The

software can read the status of the module at any time

during operation. The status information includes

FULL/EMPTY state for both transmit and receive

channels, and any other condition detected on the re-

ceived data stream, like a parity error, framing error,

data overrun, or break event.

5.4

SHARP-IR MODE

This mode supports bi-directional data communica-

tion with a remote module using infrared radiation as

the transmission medium. Sharp-IR uses Digital Am-

plitude Shift Keying (DASK) and allows serial commu-

nication 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 beginning with a zero

value start bit, an optional parity bit, and ending with

at least one stop bit with a binary value of one. A zero

is signalled by sending a 500 kHz continuous pulse

train of infrared radiation. A one is signaled by the ab-

sence of any infrared signal. The PC97338 can per-

form the modulation and demodulation operations

internally, or it can rely on the external optical module

to perform them.

Operation in Sharp-IR is similar to the operation in

UART mode. The main difference being that data

transfer operations are normally performed in half du-

plex fashion, and the modem control and status sig-

nals are not used. Selection of the Sharp-IR mode is

controlled by the 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 in non-ex-

tended 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.

5.5

IrDA 1.0 SIR MODE

This is the first operational mode that has been de-

fined by the IrDA committee and, similarly to Sharp-

IR, it also supports bi-directional data communication

with a remote module using infrared radiation as the

transmission medium. IrDA 1.0 SIR allows serial com-

munication at baud rates up to 115.2 kbaud. The for-

mat of the serial data is similar to the UART data

format. Each data word is sent serially beginning with

a zero value start bit, followed by 8 data bits, and end-

ing with at least one stop bit with a binary value of one.

A zero is signaled by sending a single infrared pulse.

A one is signaled by not sending any pulse. The width

of each pulse can be either 1.6

µs or 3/16ths of a sin-

gle bit time. (1.6

µs equals 3/16ths of a bit time at

115.2 kbaud). This way, each word begins with a

pulse for the start bit.

Operation in IrDA 1.0 SIR is similar to the operation in

UART mode. The main difference being that data

transfer operations are normally performed in half du-

plex fashion, and the modem control and status sig-

nals are not used. Selection of the IrDA 1.0 SIR mode

is controlled by the 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

in non-extended mode. This prevents legacy soft-

ware, running in non-extended mode, from spuriously

switching the module to UART mode, when the soft-

ware writes to the MCR register.

5.6

IrDA 1.1 MIR AND FIR MODES

The PC97338 supports both IrDA 1.1 MIR and FIR

modes, with data rates of 576 kbps, 1.152 Mbps and

4.0 Mbps. Details on the frame format, encoding

schemes, CRC sequences, etc. are provided in the

appropriate IrDA documents. The MIR transmitter

front-end section performs bit stuffing on the out-

bound data stream and places the Start and Stop

flags at the beginning and end of MIR frames. The

MIR receiver front-end section removes flags and “de-

stuffs” the inbound bit stream, and checks for abort

conditions.

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