MCP2120 datasheet(7/36 Pages) MICROCHIP

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DS21618B-page 7

MCP2120

2.5

Modulation

When the UART receives data to be transmitted, the

data needs to be modulated. This modulated signal

drives the IR transceiver module. Figure 2-2 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, and then the remaining 6-bit clock cycles 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.

2.6

Demodulation

The modulated signal from the IR transceiver module

needs to be demodulated to form the received data. As

demodulation occurs, the bit value is placed on the RX

pin in UART format. Figure 2-3 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, and then the

remaining 13-bit clock cycles 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 2-2:

Encoding

FIGURE 2-3:

Decoding

BITCLK

TXIR

16 CLK

Start Bit

Data bit 0

Data bit 1

Data bit 2

Data bit...

7 CLK

12 Tosc

BITCLK

RXIR

≥ 1.6 µs

13 CLK (or

≤ 50.5 µs typical)

16 CLK

8 CLK

Start Bit

Data bit 0

Data bit 1

Data bit 2

Data bit ...

(CLK)

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