© 2007 Microchip Technology Inc.

DS21618B-page 5

MCP2120

2.0

DEVICE OPERATION

The MCP2120 is a low cost infrared Encoder/Decoder.

The baud rate is user selectable to standard IrDA baud

rates between 9600 baud to 115.2 kbaud. The maxi-

mum baud rate is 312.5 kbaud.

2.1

Power-up

Any time that the device is powered up, the Device

Reset Timer delay (parameter 32) must occur before

any communication with the device is initiated. This is

from both the infrared transceiver side as well as the

controller UART interface.

2.2

Device Reset

The MCP2120 is forced into the reset state when the

RESET pin is in the low state. After the RESET pin is

brought to a high state, the Device Reset Timer occurs.

Once the DRT times out, normal operation occurs.

2.3

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 recep-

tion).

This clock is a fixed frequency, and has minimal varia-

tion in frequency (specified by crystal manufacturer).

2.4

UART Interface

The UART interface communicates with the "control-

ler". This interface is a Half duplex interface, meaning

that the system is either transmitting or receiving, but

not both at the same time.

2.4.1

BAUD RATE

The baud rate for the MCP2120 can be configured

either by the state of three hardware pins (BAUD2,

BAUD1, and BAUD0) or through software selection.

2.4.1.1

Hardware Selection

Three device pins are used to select the baud rate that

the MCP2120 will transmit and receive data. These

pins are called BAUD2, BAUD1, and BAUD0. There is

one pin state (device mode) where the application soft-

ware can specify the baud rate. Table 2-1 shows the

baud rate configurations.

TABLE 2-1:

HARDWARE BAUD RATE SELECTION VS. FREQUENCY

BAUD2:BAUD0

Frequency (MHz)

Bit Rate

2.000

3.6864

4.9152

7.3728

000

800

2604

4800

6400

9600

19200

26042

001

1600

5208

9600

12800

19200

38400

52083

010

3200

10417

19200

25600

38400

78600

104167

011

4800

15625

28800

38400

57600

115200

156250

100

9600

31250

57600

78600

115200

230400

312500

Note 1: An external clock is recommended for frequencies below 2 MHz.

2: For frequencies above 7.5 MHz, the TXIR pulse width (parameter IR121) will be shorter than the minimum

pulse width of 1.6 µs in the IrDA standard specification.