MCP2155_13 datasheet(19/52 Pages) MICROCHIP

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Preliminary

DS21690B-page 19

MCP2155

2.11

Turnaround Latency

An IR link can be compared to a one-wire data connec-

tion. The IR transceiver can transmit or receive, but not

both at the same time. A delay of one bit time is sug-

gested between the time a byte is received and another

byte is transmitted.

2.12

IR Port Baud Rate

The baud rate for the MCP2155 IR port (the TXIR and

RXIR pins) is initially at the default rate of 9600 baud.

The Host controller will determine the maximum baud

rate that the MCP2155 can support. This information is

used during NDM with the Primary device to set the

baud rate of the IR link. The maximum IR baud rate is

not required to be the same as the MCP2155’s serial

port (UART) baud rate (as determined by the

BAUD1:BAUD0 pins).

2.13

Programmable Device ID

The MCP2155 has a flexible feature that allows the

MCP2155 Device ID to be changed by the Host control-

ler. The default ID is “Generic IrDA”, and is stored in

non-volatile electrically erasable programmable mem-

ory (EEPROM). The maximum ID String length is 19

bytes. The format of the ID EEPROM is shown in

Figure 2-11.

The ID String must only contain the ASCII characters

from 20h to 7Ah (inclusive).

The MCP2155 enters into ID String programming when

the MCP2155 exits the reset state and detects that the

DTR pin is High and the RTS pin is Low.

A Host controller connected to the MCP2155 would

typically do the following steps to place the MCP2155

into ID String programming mode:

Force the MCP2155 into reset (RESET pin

forced Low).

Force the DTR pin High and the RTS pin Low.

Release the MCP2155 from reset (RESET pin

forced High).

Once the MCP2155 is ready to receive data, the CTS

pin will be forced low. Data may now be transferred, fol-

lowing the format in Figure 2-11. The CTS pin deter-

mines the flow control, and the Host controller must

monitor this signal to ensure that the data byte may be

sent.

Once the Host controller has sent its last byte, the DTR

pin must be set Low. This ensures that if another reset

occurs, the MCP2155 will not re-enter ID String pro-

gramming mode. The MCP2155 uses the String Length

(1st byte transmitted) to determine when to ID String

programming mode has completed. This returns the

MCP2155 to normal operation.

Example 2-1 show the firmware code for a PIC16Cxxx

acting as the Host controller to modify the MCP2155

Device ID String.

FIGURE 2-11:

ID STRING FORMAT

Note 1: If a non-valid ID String (contains an ASCII

character

not

the

valid

range)

programmed, the MCP2155 will not create

a link with a primary device.

2: The communication program that is sup-

plied with Microsoft Windows operating sys-

tem (called Hyper Terminal), may leave the

DTR signal High and the RTS signals Low

when the program disconnects, or is closed.

Care should be taken to ensure that this

could not accidently cause the MCP2155 to

enter Device ID Sting Programming.

Length

ID String

1 Byte

1 to 19 Bytes

1st Byte

Transferred

Last Byte

Transferred

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