CP3BT26

UPEN

The Parity Enable bit enables or disables par-

 

ity generation and parity checking. When the

 

UART is configured to transmit nine data bits

 

per frame, there is no parity bit and the Un-

 

PEN bit is ignored.

 

0

– Parity generation and checking disabled.

 

1

– Parity generation and checking enabled.

22.3.6UART Mode Select Register 1 (UnMDSL1)

The UnMDSL1 register is a byte-wide, read/write register that selects the clock source, synchronization mode, atten- tion mode, and line break generation. This register is cleared at reset. The register format is shown below.

7

6

 

5

4

 

3

 

2

1

 

0

URTS

UFCE

UERD

UETD

UCKS

UBRK

UATN

UMOD

 

 

 

 

 

 

 

 

UMOD

The Mode bit selects between synchronous

 

and asynchronous mode. Synchronous mode

 

is only available for the UART0 module.

 

 

0

– Asynchronous mode.

 

 

 

 

 

1

– Synchronous mode.

 

 

 

 

UATN

The Attention Mode bit is used to enable At-

 

tention mode. When set, this bit selects the at-

 

tention mode of operation for the UART. When

 

clear, the attention mode is disabled. The

 

hardware clears this bit after an address

 

frame is received. An address frame is a 9-bit

 

character with a 1 in the ninth bit position.

 

0

– Attention mode disabled.

 

 

 

 

1

– Attention mode enabled.

 

 

 

UBRK

The Force Transmission Break bit is used to

 

force the TXD output low. Setting this bit to 1

 

causes the TXD pin to go low. TXD remains

 

low until the UBRK bit is cleared by software.

 

0

– Normal operation.

 

 

 

 

 

1

– TXD pin forced low.

 

 

 

 

UCKS

The Synchronous Clock Source bit controls

 

the clock source when the UART operates in

 

the synchronous mode (UMOD = 1). This

 

functionality is only available for the UART0

 

module. If the UCKS bit is set, the UART op-

 

erates from an external clock provided on the

 

CKX pin. If the UCKS bit is clear, the UART

 

operates from the baud rate clock produced

 

by the UART on the CKX pin. This bit is ig-

 

nored when the UART operates in the asyn-

 

chronous mode.

 

 

 

 

 

 

 

0

– Internal baud rate clock is used.

 

 

1

– External clock is used.

 

 

 

UETD

The Enable Transmit DMA bit controls wheth-

 

er DMA is used for UART transmit operations.

 

Enabling transmit DMA automatically disables

 

transmit interrupts, without regard to the state

 

of the UETI bit.

 

 

 

 

 

 

 

0

– Transmit DMA disabled.

 

 

 

 

1

– Transmit DMA enabled.

 

 

 

UERD

The Enable Receive DMA bit controls whether

 

DMA is used for UART receive operations.

 

Enabling receive DMA automatically disables

 

receive interrupts, without regard to the state

 

of the UERI bit. Receive error interrupts are

 

unaffected by the UERD bit.

 

0

– Receive DMA disabled.

 

1

– Receive DMA enabled.

UFCE

The Flow Control Enable bit controls whether

 

flow control interrupts are enabled.

 

0

– Flow control interrupts disabled.

 

1

– Flow control interrupts enabled.

URTS

The Ready To Send bit directly controls the

 

state of the

RTS

output.

 

0

RTS

output is high.

 

1

RTS

output is low.

22.3.7UART Status Register (UnSTAT)

The UnSTAT register is a byte-wide, read-only register that contains the receive and transmit status bits. This register is cleared upon reset. Any attempt by software to write to this register is ignored. The register format is shown below.

7

6

5

4

3

 

2

1

 

0

Res.

UXMIP

URB9

UBKD

UERR

UDOE

UFE

UPE

 

 

 

 

 

 

 

 

UPE

The Parity Error bit indicates whether a parity

 

error is detected within a received character.

 

This bit is automatically cleared by the hard-

 

ware when the UnSTAT register is read.

 

 

0

– No parity error occurred.

 

 

 

 

 

1

– Parity error occurred.

 

 

 

 

UFE

The Framing Error bit indicates whether the

 

UART fails to receive a valid stop bit at the end

 

of a frame. This bit is automatically cleared by

 

the hardware when the UnSTAT register is

 

read.

 

 

 

 

 

 

 

 

0

– No framing error occurred.

 

 

 

 

1

– Framing error occurred.

 

 

 

 

UDOE

The Data Overrun Error bit is set when a new

 

character is received and transferred to the

 

UnRBUF register before software has read

 

the previous character from the UnRBUF reg-

 

ister. This bit is automatically cleared by the

 

hardware when the UnSTAT register is read.

 

0

– No receive overrun error occurred.

 

 

1

– Receive overrun error occurred.

 

UERR

The Error Status bit indicates when a parity,

 

framing, or overrun error occurs (any time that

 

the UPE, UFE, or UDOE bit is set). It is auto-

 

matically cleared by the hardware when the

 

UPE, UFE, and UDOE bits are all 0.

 

 

0

– No receive error occurred.

 

 

 

 

1

– Receive error occurred.

 

 

 

 

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National CP3BT26 manual Uart Mode Select Register 1 UnMDSL1, Uart Status Register UnSTAT