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CS8130-CS_94

Multi-Standard Infrared Transceiver

Cirrus Logic 

CS8130

Mode 3 (TV remote) Receive Choices

The modulation frequency must be set into the

modulator divider registers. The tolerance on the

expected frequency must be programmed into

the Receive ASK Timing Sensitivity (RATS) reg-

ister. The RATS register sets the time window

that the demodulator will accept for the period of

valid data. Since the RATS register specifies

time windows which are negative (e.g. 1000b (8)

= +0.27 µs to -4.61 µs), then the modulation

frequency must be set to lower than the desired

nominal setting. For example, with RATS set to

1000 (8), and the desired nominal frequency be-

ing 38 kHz, then set the modulation divider

registers to 35.10 kHz. With these settings, the

demodulator will accept any frequency from

34.78 kHz to 41.88 kHz as valid. Smaller RATS

register settings will result in tighter tolerance on

the accepted receive modulation frequency.

Changes in the RATS register settings must be

accompanied by changes in the modulation fre-

quency register to keep the nominal desired

frequency in the center of the valid frequency

band.

There are two TV remote receive data modes:

"oversampled" mode and "programmed T pe-

riod" mode. For "oversampled" mode, first

choose the UART to CS8130 baud rate, typically

115.2 kbps. Then set the TV remote receive tim-

ing register to a rate which is less than 80% of

the UART baud rate. The CS8130 will now start

sampling the demodulated infrared data at the

TV remote receive sample rate. The stream of

samples will be assembled into characters, with a

start bit and a stop bit, and will be transmitted to

the UART via RXD at the UART baud rate. The

system software can then concatenate successive

characters and reconstruct the incoming bit

stream.

"Programmed T period" mode requires that the

bit period of the bursts of modulated carrier be

known. This period is programmed into the TV

remote receive timing registers. The UART to

CS8130 baud rate must be set to at least 20%

greater than 1/T. The CS8130 will now use the

edges of the demodulated incoming infrared data

to indicate each bit state. For continuous periods

of low or high, the CS8130 will sample the level

in the center of each incoming bit period (using

T as the bit period). Any transition will reset the

timer that is used for the sampling process,

thereby eliminating errors caused by the sample

timing being different to the incoming bit period.

Characters are assembled and sent to the UART

every 8 bits (see Figure 6).

If the T period is not known, it is possible to

measure T by using "oversampled" mode, and

LIGHT

INPUT

1/2400

1 0 1 1 0 0 1 1 1 0 0 1 1 0 0 1 0 0 1 LIGHT

NO LIGHT

RXD*

RXD*

10110011

8 data bits

Start

Bit

Stop

Bit

*RXD Baud rate can be set

from 4800 to 115200 bps

Figure 6. Mode 3 (TV remote) Receive Data Format

10

DS134PP2

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