MCP2155 datasheet(5/34 Pages) MICROCHIP

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 2004 Microchip Technology Inc.

Preliminary

DS21894B-page 5

MCP2122

2.0

DEVICE OPERATION

The MCP2122 is a low-cost infrared encoder/decoder.

The baud rate is the same for the host UART and IR

interfaces and is determined by the frequency of the

16XCLK signal, with a maximum baud rate of

115.2 Kbaud.

The MCP2122 is made up of these functional modules:

• Clock Driver (16XCLK)

• Reset

• IR Encoder/Decoder

- IrDA Standard Encoder

- IrDA Standard Decoder

The 16XCLK circuit allows a clock input to provide the

device clock.

The Reset circuit supports an external reset signal.

The IR Encoder logic takes a data bit and converts it to

the IrDA standard signal according to the IrDA standard

Physical Layer specification, while the IR Decoder

logic takes the IrDA standard signal and converts it to

8-bit data bytes.

2.1

Power-up

As the device is powered up, there will be a voltage

range in which the device will not operate properly. The

device should be reset once it has entered the normal

operating range (from an out-of-voltage condition). The

RESET pin may then be forced high.

Other device operating parameters (such as frequency,

temperature, etc.) must also be within their operating

ranges when the device exits reset. Otherwise, the

device may not function as desired.

2.2

Device Reset

The MCP2122 is forced into the known state (RESET)

when the RESET pin is in the low state. Once the

RESET pin is brought to a high state, the device begins

normal operation (if the device operating parameters

are met). Table 2-1 shows the states of the output pins

while the device is in reset (RESET = Low). Table 2-2

shows the state of the output pins once the device exits

reset, RESET = L

→H (device in Normal Operation

mode).

The MCP2122 has a RESET noise filter in the RESET

input signal path. The filter will detect and ignore small

pulses.

Using the RESET pin to enter a low-power state is

discussed in Section 2.9 “Minimizing Power”.

TABLE 2-1:

DEFAULT OUTPUT PIN

STATES IN DEVICE RESET

TABLE 2-2:

DEFAULT OUTPUT PIN

STATES AFTER DEVICE

RESET (RESET = L

→H)

2.3

Decoupling

It is highly recommended that the MCP2122 have a

decoupling capacitor (CBYP). A 0.01 µF capacitor is

recommended as a starting value, but an evaluation of

the best value for your circuit/layout should be

performed. Place this decoupling capacitor (CBYP) as

close to the MCP2122 as possible (see Figure 2-1).

FIGURE 2-1:

DEVICE DECOUPLING

Input Pin

Output Pin

State

Comments

Name

State

TXIR

RESET

Device in Reset mode

Input Pin

Output Pin

State

Comments

Name State

TXIR

—

→H

→L

After 7 - 8 16XCLK

pulses, the TXIR pin

will pulse high.

H—

RXIR

→L

—

After 4 16XCLK pulses,

RX = L.

—

VDD

(bypass

capacitor)

MCP2122

VDD

RESET

VSS

16XCLK

TXIR

RXIR

CBYP

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