MCP2140-IP datasheet(11/58 Pages) MICROCHIP

11 / 58 page

 2003 Microchip Technology Inc.

Preliminary

DS21790A-page 11

MCP2140

2.5

Encoder/Decoder

The encoder converts the UART format data into the

IrDA Standard format data and the decoder converts

IrDA Standard format data into UART format data.

2.5.1

ENCODER (MODULATION)

The data that the MCP2140 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 2-5 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, 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 µsec (see Parameter IR121). The

remaining 6-bit clock cycles will be low. If the value to

transmit is a logic-high, the TXIR pin will output a low

level for the entire 16-bit clock cycles.

FIGURE 2-5:

ENCODING

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 2-5. The TX bit value is shown to

represent the value to be transmitted on

the TXIR 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

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