P16F877 datasheet(97/218 Pages) MICROCHIP

97 / 218 page

 2001 Microchip Technology Inc.

DS30292C-page 95

PIC16F87X

10.0

ADDRESSABLE UNIVERSAL

SYNCHRONOUS

ASYNCHRONOUS RECEIVER

TRANSMITTER (USART)

The Universal Synchronous Asynchronous Receiver

Transmitter (USART) module is one of the two serial

I/O modules. (USART is also known as a Serial Com-

munications Interface or SCI.) The USART can be con-

figured as a full duplex asynchronous system that can

communicate with peripheral devices such as CRT ter-

minals and personal computers, or it can be configured

as a half duplex synchronous system that can commu-

nicate with peripheral devices such as A/D or D/A inte-

grated circuits, serial EEPROMs etc.

The USART can be configured in the following modes:

• Asynchronous (full duplex)

• Synchronous - Master (half duplex)

• Synchronous - Slave (half duplex)

Bit SPEN (RCSTA<7>) and bits TRISC<7:6> have to

be set in order to configure pins RC6/TX/CK and

RC7/RX/DT as the Universal Synchronous Asynchro-

nous Receiver Transmitter.

The USART module also has a multi-processor com-

munication capability using 9-bit address detection.

TXSTA: TRANSMIT STATUS AND CONTROL REGISTER (ADDRESS 98h)

R/W-0

U-0

R/W-0

R-1

R/W-0

CSRC

TX9

TXEN

SYNC

—

BRGH

TRMT

TX9D

bit 7

bit 0

bit 7

CSRC: Clock Source Select bit

Asynchronous mode:

Don’t care

Synchronous mode:

= Master mode (clock generated internally from BRG)

= Slave mode (clock from external source)

bit 6

TX9: 9-bit Transmit Enable bit

= Selects 9-bit transmission

= Selects 8-bit transmission

bit 5

TXEN: Transmit Enable bit

= Transmit enabled

= Transmit disabled

Note: SREN/CREN overrides TXEN in SYNC mode.

bit 4

SYNC: USART Mode Select bit

= Synchronous mode

= Asynchronous mode

bit 3

Unimplemented: Read as '0'

bit 2

BRGH: High Baud Rate Select bit

Asynchronous mode:

= High speed

= Low speed

Synchronous mode:

Unused in this mode

bit 1

TRMT: Transmit Shift Register Status bit

= TSR empty

= TSR full

bit 0

TX9D: 9th bit of Transmit Data, can be parity bit

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

- n = Value at POR

’1’ = Bit is set

’0’ = Bit is cleared

x = Bit is unknown

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