DVR21 datasheet(232/416 Pages) MICROCHIP

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DS30010118D-page 232

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19.2

Transmitting in 8-Bit Data Mode

Set up the UARTx:

Write appropriate values for data, parity and

Stop bits.

Write appropriate baud rate value to the

UxBRG register.

Set up transmit and receive interrupt enable

and priority bits.

Enable the UARTx.

Set the UTXEN bit (causes a transmit interrupt,

two cycles after being set).

Write a data byte to the lower byte of the

UxTXREG 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.

Alternatively, 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 bits, UTXISEL<1:0>.

19.3

Transmitting in 9-Bit Data Mode

Set up the UARTx (as described in Section 19.2

“Transmitting in 8-Bit Data Mode”).

Enable the UARTx.

Set the UTXEN bit (causes a transmit interrupt).

Write UxTXREG as a 16-bit value only.

A word write to UxTXREG 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 bits, UTXISELx.

19.4

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 UARTx for the desired mode.

Set UTXEN and UTXBRK to set up the Break

character.

Load the UxTXREG with a dummy character to

initiate transmission (value is ignored).

Write ‘55h’ to UxTXREG; this 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.

19.5

Receiving in 8-Bit or 9-Bit Data

Mode

Set up the UARTx (as described in Section 19.2

“Transmitting in 8-Bit Data Mode”).

Enable the UARTx by setting the URXEN bit

(UxSTA<12>).

A receive interrupt will be generated when one

or more data characters have been received as

per interrupt control bits, URXISEL<1:0>.

Read the OERR bit to determine if an overrun

error has occurred. The OERR bit must be reset

in software.

Read UxRXREG.

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.

19.6

Operation of UxCTS and UxRTS

Control Pins

UARTx Clear-to-Send (UxCTS) and Request-to-Send

(UxRTS) are the two hardware controlled pins that are

associated with the UARTx modules. These two pins

allow the UARTx to operate in Simplex and Flow

Control mode. They are implemented to control the

transmission and reception between the Data Terminal

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

19.7

Infrared Support

The UARTx 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 is the full implementa-

tion of the IrDA encoder and decoder. Note that

because the IrDA modes require a 16x baud clock, they

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

19.7.1

IrDA CLOCK OUTPUT FOR

EXTERNAL IrDA SUPPORT

To support external IrDA encoder and decoder devices,

the BCLKx pin (same as the UxRTS pin) can be

configured to generate the 16x baud clock. When

UEN<1:0> = 11, the BCLKx pin will output the

16x baud clock if the UARTx module is enabled; it can

be used to support the IrDA codec chip.

19.7.2

BUILT-IN IrDA ENCODER AND

DECODER

The UARTx has full implementation of the IrDA

encoder and decoder as part of the UARTx module.

The built-in IrDA encoder and decoder functionality is

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

enabled (IREN = 1), the receive pin (UxRX) acts as the

input from the infrared receiver. The transmit pin

(UxTX) acts as the output to the infrared transmitter.

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