PIC24F04KA201 datasheet(137/224 Pages) MICROCHIP

137 / 224 page

Preliminary

DS39937B-page 135

PIC24F04KA201 FAMILY

17.2

Transmitting in 8-Bit Data Mode

Set up the UART:

Write appropriate values for data, parity and

Stop bits.

Write appropriate baud rate value to the

U1BRG register.

Set up transmit and receive interrupt enable

and priority bits.

Enable the UART.

Set the UTXEN bit (causes a transmit interrupt

two cycles after being set).

Write data byte to lower byte of U1TXREG word.

The value will be immediately transferred to the

Transmit Shift Register (TSR), and the serial bit

stream will start shifting out with the next rising

edge of the baud clock.

Alternately, the data byte may be transferred

while UTXEN = 0, and then, the user may set

UTXEN. This will cause the serial bit stream to

begin immediately because the baud clock will

start from a cleared state.

A transmit interrupt will be generated as per

interrupt control bit, UTXISEL1.

17.3

Transmitting in 9-Bit Data Mode

Set up the UART (as described in Section 17.2

“Transmitting in 8-Bit Data Mode”

Enable the UART.

Set the UTXEN bit (causes a transmit interrupt

two cycles after being set).

Write U1TXREG as a 16-bit value only.

A word write to U1TXREG triggers the transfer

of the 9-bit data to the TSR. The serial bit stream

will start shifting out with the first rising edge of

the baud clock.

A transmit interrupt will be generated as per the

setting of control bit, UTXISEL1.

17.4

Break and Sync Transmit

Sequence

The following sequence will send a message frame

header made up of a Break, followed by an auto-baud

Sync byte.

Configure the UART for the desired mode.

Set UTXEN and UTXBRK – sets up the Break

character.

Load the U1TXREG with a dummy character to

initiate transmission (value is ignored).

Write ‘55h’ to U1TXREG – loads the Sync

character into the transmit FIFO.

After the Break has been sent, the UTXBRK bit

is reset by hardware. The Sync character now

transmits.

17.5

Receiving in 8-Bit or 9-Bit Data

Mode

Set up the UART (as described in Section 17.2

“Transmitting in 8-Bit Data Mode”

Enable the UART.

A receive interrupt will be generated when one

or more data characters have been received as

per interrupt control bit, URXISEL1.

Read the OERR bit to determine if an overrun

error has occurred. The OERR bit must be reset

in software.

Read U1RXREG.

The act of reading the UxRXREG character will move

the next character to the top of the receive FIFO,

including a new set of PERR and FERR values.

17.6

Operation of U1CTS and U1RTS

Control Pins

UART1 Clear to Send (U1CTS) and Request to Send

(U1RTS) are the two hardware-controlled pins that are

associated with the UART module. These two pins

allow the UART to operate in Simplex and Flow Control

modes. They are implemented to control the

transmission and reception between the Data Terminal

Equipment (DTE). The UEN<1:0> bits in the U1MODE

17.7

Infrared Support

The UART module provides two types of infrared UART

support: one is the IrDA clock output to support an

external IrDA encoder and decoder device (legacy

module

support),

and

the

other

the

full

implementation of the IrDA encoder and decoder.

As the IrDA modes require a 16x baud clock, they will

only work when the BRGH bit (U1MODE<3>) is ‘0’.

17.7.1

EXTERNAL IrDA SUPPORT – IrDA

CLOCK OUTPUT

To support external IrDA encoder and decoder devices,

the U1BCLK pin (same as the U1RTS pin) can be

configured to generate the 16x baud clock. When

UEN<1:0> = 11, the U1BCLK pin will output the 16x

baud clock if the UART module is enabled; it can be

used to support the IrDA codec chip.

17.7.2

BUILT-IN IrDA ENCODER AND

DECODER

The UART has full implementation of the IrDA encoder

and decoder as part of the UART module. The built-in

IrDA encoder and decoder functionality is enabled

using the IREN bit (U1MODE<12>). When enabled

(IREN = 1), the receive pin (U1RX) acts as the input

from the infrared receiver. The transmit pin (U1TX) acts

as the output to the infrared transmitter.

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