DSPIC30F2012AT20ESLASHML datasheet(105/205 Pages) MICROCHIP

105 / 205 page

DS70139E-page 103

dsPIC30F2011/2012/3012/3013

15.2

Enabling and Setting Up UART

15.2.1

ENABLING THE UART

The UART module is enabled by setting the UARTEN

bit in the UxMODE register (where x = 1 or 2). Once

enabled, the UxTX and UxRX pins are configured as an

output and an input respectively, overriding the TRIS

and LAT register bit settings for the corresponding I/O

port pins. The UxTX pin is at logic ‘1’ when no

transmission is taking place.

15.2.2

DISABLING THE UART

The UART module is disabled by clearing the UARTEN

bit in the UxMODE register. This is the default state

after any Reset. If the UART is disabled, all I/O pins

operate as port pins under the control of the LAT and

TRIS bits of the corresponding port pins.

Disabling the UART module resets the buffers to empty

states. Any data characters in the buffers are lost and

the baud rate counter is reset.

All error and status flags associated with the UART

module are reset when the module is disabled. The

URXDA, OERR, FERR, PERR, UTXEN, UTXBRK and

UTXBF bits are cleared, whereas RIDLE and TRMT

are

set.

Other

control

bits,

including

ADDEN,

URXISEL<1:0>, UTXISEL, as well as the UxMODE

and UxBRG registers, are not affected.

Clearing the UARTEN bit while the UART is active will

abort all pending transmissions and receptions and

reset the module as defined above. Re-enabling the

UART will restart the UART in the same configuration.

15.2.3

ALTERNATE I/O

The alternate I/O function is enabled by setting the

ALTIO bit (UxMODE<10>). If ALTIO = 1, the UxATX

and UxARX pins (alternate transmit and alternate

receive pins, respectively) are used by the UART mod-

ule instead of the UxTX and UxRX pins. If ALTIO = 0,

the UxTX and UxRX pins are used by the UART

module.

15.2.4

SETTING UP DATA, PARITY AND

STOP BIT SELECTIONS

Control bits PDSEL<1:0> in the UxMODE register are

used to select the data length and parity used in the

transmission. The data length may either be 8 bits with

even, odd or no parity, or 9 bits with no parity.

The STSEL bit determines whether one or two Stop bits

will be used during data transmission.

The default (power-on) setting of the UART is 8 bits, no

parity and 1 Stop bit (typically represented as 8, N, 1).

15.3

Transmitting Data

15.3.1

TRANSMITTING IN 8-BIT DATA

MODE

The following steps must be performed in order to

transmit 8-bit data:

Set up the UART:

First, the data length, parity and number of Stop

bits must be selected. Then, the transmit and

receive interrupt enable and priority bits are

setup in the UxMODE and UxSTA registers.

Also, the appropriate baud rate value must be

written to the UxBRG register.

Enable the UART by setting the UARTEN bit

(UxMODE<15>).

Set the UTXEN bit (UxSTA<10>), thereby

enabling a transmission.

Write the byte to be transmitted to the lower byte

of UxTXREG. The value will be transferred to the

Transmit Shift register (UxTSR) immediately

and the serial bit stream will start shifting out

during the next rising edge of the baud clock.

Alternatively, the data byte may be written while

UTXEN = 0, following which, 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, depend-

ing on the value of the interrupt control bit

UTXISEL (UxSTA<15>).

15.3.2

TRANSMITTING IN 9-BIT DATA

MODE

The sequence of steps involved in the transmission of

9-bit data is similar to 8-bit transmission, except that a

16-bit data word (of which the upper 7 bits are always

clear) must be written to the UxTXREG register.

15.3.3

TRANSMIT BUFFER (UXTXB)

The transmit buffer is 9 bits wide and 4 characters

deep. Including the Transmit Shift register (UxTSR),

the user effectively has a 5-deep FIFO (First-In, First-

Out) buffer. The UTXBF bit (UxSTA<9>) indicates

whether the transmit buffer is full.

If a user attempts to write to a full buffer, the new data

will not be accepted into the FIFO and no data shift will

occur within the buffer. This enables recovery from a

buffer overrun condition.

The FIFO is reset during any device Reset, but is not

affected when the device enters or wakes up from a

Power Saving mode.

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