MCP2140-ISO datasheet(12/58 Pages) MICROCHIP

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MCP2140

DS21790A-page 12

Preliminary

 2003 Microchip Technology Inc.

2.5.2

DECODER (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). Once demodula-

tion of the data byte occurs, the data that is received is

transmitted by the MCP2140 UART (on the RX pin).

Figure 2-6 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, the RXIR pin will be a low

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

1.6 µs. 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, 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.

2.6

IR Port Baud Rate

The baud rate for the MCP2140 IR port (the TXIR and

RXIR pins) is fixed at the default rate of 9600 baud. The

Primary device will be informed of this parameter dur-

ing NDM. The Host UART baud rate and the IR port

baud rate are the same.

FIGURE 2-6:

DECODING

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 2-6. The RXIR bit value is shown to

represent the value to be transmitted on

the RX pin.

BITCLK

RXIR Bit Value

≥ 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)

RXPD

RXPDREF

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