CS8130-CS datasheet(9/28 Pages) CIRRUS

9 / 28 page

The modulation frequency is determined by the

modulator divider registers. The transmit bit rate

is determined by the TV Remote transmit bit rate

divider. The UART to CS8130 baud rate must be

set to at least 20% faster than the transmit bit

rate.

Receive Path

A PIN diode is attached to the PINA and PINC

pins. Compensation for the DC ambient light is

applied to the photocurrent from the diode. The

change in photocurrent from ambient is ampli-

fied and compared to a threshold value. If the

photocurrent is greater than the set threshold, the

output is set to ’light’. If the photocurrent is less

than the set threshold, the output is set to ’no

light’. The threshold current is programmable.

This allows users to make the tradeoff between

noise immunity and the reliable transmission dis-

tance of the link. The PIN diode amplifier has a

bandpass filter characteristic, to limit the effects

of IR interference. The resulting logic signal is

further qualified, depending on the IR format se-

lected.

An autodetect feature is provided. If autodetect

mode is enabled, and transmit TV remote mode

is disabled, the FORM/BSY output pin indicates

the format of incoming data. If high, then the

incoming data is in IrDA/HPSIR format. If low,

the data is in ASK format which matches the

programmed modulation frequency.

Mode 1 (IrDA) Receive Choices

For Mode 1a, a logic circuit is set to only look

for pulse widths of 1.6

µs. For Mode 1b, a logic

circuit looks for pulses of 3/16 of the set baud

rate bit period. For Mode 1c, a logic circuit

looks for pulse widths of

≥1.6 µs, but ≤3/16 of

the set baud rate bit period.

Mode 2 (ASK) Receive Choices

For Mode 2, a logic circuit looks for sequences

of ’light’ and ’no light’ which matches the ex-

pected 500kHz carrier.

The modulator divider

registers must be set to 6. The ASK receive tim-

ing sensitivity register should be set to 0,

yielding a valid incoming frequency range of

461 kHz to 614 kHz.

The RXD data transitions will lag behind the in-

frared activity by 3 modulation cycles. This

allows the modulation detect circuit time to ver-

ify the correct modulation frequency.

Start

Bit

Stop

Bit

1/2400

OFF

* TXD Baud rate can be set

from 4800 to 115200 bps

LED

OUTPUT

FORM/BSY

TXD*

Figure 5. Mode 3 (TV Remote) Transmit Data Format

CS8130

DS134PP2

CS8130

DS134F1

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