MCP2140A データシートの表示（PDF） - Microchip Technology

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MCP2140A

IrDA® Standard Protocol Stack Controller With Fixed 9600 Baud Communication Rate

Microchip Technology 

MCP2140A

2.3.1.1

Crystal Oscillator / Ceramic

Resonators

A crystal or ceramic resonator can be connected to the

OSC1 and OSC2 pins to establish oscillation (refer to

Figure 2-1). The MCP2140A oscillator design requires

the use of a parallel-cut crystal. Use of a series cut

crystals may give a frequency outside of the crystal

manufacturers specifications.

FIGURE 2-1:

CRYSTAL OPERATION

(CERAMIC RESONATOR)

Ceramic

Resonator

OSC1

C1

XTAL

OSC2

RS

C2

(Note)

To internal

logic

RF

MCP2140A

See Table 2-1 and Table 2-2 for recommended

values of C1 and C2.

Note: A series resistor may be required for

AT strip cut crystals.

TABLE 2-1: CAPACITOR SELECTION FOR

CERAMIC RESONATORS

Freq

OSC1 (C1) OSC2 (C2)

3.6864 MHz

10 - 22 pF

10 - 22 pF

Note:

Higher capacitance increases the stability

of the oscillator, but also increases the

start-up time. These values are for design

guidance only. Since each resonator has

its own characteristics, the user should

consult the resonator manufacturer for

appropriate values of external

components.

TABLE 2-2: CAPACITOR SELECTION FOR

CRYSTAL OSCILLATOR

Freq

OSC1 (C1)

OSC2 (C2)

3.6864 MHz

15 - 30 pF

15 - 30 pF

Note:

Higher capacitance increases the stability

of the oscillator but also increases the

start-up time. These values are for design

guidance only. RS may be required to

avoid overdriving crystals with low drive

level specification. Since each crystal has

its own characteristics, the user should

consult the crystal manufacturer for

appropriate values of external

components.

2.3.1.2 External Clock

For applications where a clock is already available

elsewhere, users may directly drive the MCP2140A

provided that this external clock source meets the AC/

DC timing requirements listed in Section 4.3 “Timing

Diagrams and Specifications”. Figure 2-2 shows

how an external clock circuit should be configured.

FIGURE 2-2:

EXTERNAL CLOCK

Clock From

external

system

Open

OSC1MCP2140A

OSC2

2.3.2 BIT CLOCK

The device crystal is used to derive the communication

bit clock (BITCLK). There are 16 BITCLKs for each bit

time. The BITCLKs are used for the generation of the

start bit and the eight data bits. The stop bit uses the

BITCLK when the data is transmitted (not for

reception).

This clock is a fixed-frequency and has minimal

variation in frequency (specified by the crystal

manufacturer).

DS22050A-page 8

© 2007 Microchip Technology Inc.

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