MCP2155_13 datasheet(9/52 Pages) MICROCHIP

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Preliminary

DS21690B-page 9

MCP2155

2.6

Modulation

The data that the MCP2155 UART received (on the TX

pin) that needs to be transmitted (on the TXIR pin), will

need to be modulated. This modulated signal drives the

IR transceiver module. Figure 2-3 shows the encoding

of the modulated signal.

Each bit time is comprised of 16-bit clocks. If the value

to be transmitted (as determined by the TX pin) is a

logic low, then the TXIR pin will output a low level for

7-bit clock cycles, a logic high level for 3-bit clock

cycles or a minimum of 1.6

S (see parameter IR121),

and then the remaining 6-bit clock cycles (or difference

up to the 16-bit clock time) will be low. If the value to

transmit is a logic high, then the TXIR pin will output a

low level for the entire 16-bit clock cycles.

2.7

Demodulation

The modulated signal (data) from the IR transceiver

module (on RXIR pin) needs to be demodulated to form

the received data (on RX pin). After demodulation of

the data byte occurs, the data that is received is trans-

mitted by the MCP2155 UART (on the RX pin).

Figure 2-4 shows the decoding of the modulated

signal.

Each bit time is comprised of 16 bit clocks. If the value

to be received is a logic low, then the RXIR pin will be

a low level for the first 3-bit clock cycles or a minimum

of 1.6 µs, and then the remaining 13-bit clock cycles (or

difference up to the 16-bit clock time) will be high. If the

value to be received is a logic high, then the RXIR pin

will be a high level for the entire 16-bit clock cycles. The

level on the RX pin will be in the appropriate state for

the entire 16 clock cycles.

FIGURE 2-3:

ENCODING

FIGURE 2-4:

DECODING

Note:

The signal on the TXIR pin does not actu-

ally line up in time with the bit value that

was transmitted on the TX pin as shown in

Figure 2-3. The TX bit value is shown to

represent the value to be transmitted on

the TXIR pin.

Note:

The signal on the RX pin does not actually

line up in time with the bit value that was

received on the RXIR pin as shown in

Figure 2-4. The RXIR bit value is shown to

represent the value to be transmitted on

the RX pin.

BITCLK

TX Bit

TXIR

16 CLK

7 CLK

Start Bit

Data bit 0

Data bit 1

Data bit 2

Data bit ...

24 Tosc

Value

BITCLK

RXIR Bit

 1.6 µs (up to 3 CLK)

 13 CLK

16 CLK

Start Bit

Data bit 0

Data bit 1

Data bit 2

Data bit ...

(CLK)

Value

21690B.book Page 9 Thursday, January 10, 2013 1:06 PM

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