PIC16F688-ESLASHST datasheet(79/174 Pages) MICROCHIP

79 / 174 page

 2004 Microchip Technology Inc.

Preliminary

DS41203B-page 77

PIC16F688

10.0

ENHANCED UNIVERSAL

ASYNCHRONOUS RECEIVER

TRANSMITTER (EUSART)

The Enhanced Universal Synchronous Asynchronous

Receiver Transmitter (EUSART) module is the serial

I/O module available for PIC16F688 . (EUSART is also

known as a Serial Communications Interface or SCI).

The EUSART can be configured as a full-duplex

asynchronous system that can communicate with

peripheral devices, such as CRT terminals and

personal computers. It can also be configured as a

half-duplex synchronous system that can communicate

with peripheral devices, such as A/D or D/A integrated

circuits, serial EEPROMs, etc.

The EUSART module implements additional features,

including

automatic

baud

rate

detection

and

calibration, automatic wake-up on Break reception and

13-bit Break character transmit. These make it ideally

suited for use in Local Interconnect Network (LIN) bus

systems.

The USART can be configured in the following modes:

• Asynchronous (full-duplex) with:

- Auto-wake-up on Break

- Auto baud calibration

- 13-bit Break character transmission

• Synchronous – Master (half-duplex) with

selectable clock polarity

• Synchronous – Slave (half-duplex) with selectable

clock polarity

In order to configure pins RC4/C2OUT/TX/CK and

RC5/RX/DT

the

Universal

Synchronous

Asynchronous Receiver Transmitter:

• SPEN (RCSTA<7>) bit must be set (= 1),

• TRISC<5> bit must be set (= 1), and

• TRISC<4> bit must be set (= 1).

The operation of the EUSART module is controlled

through three registers:

• Transmit Status and Control (TXSTA)

• Receive Status and Control (RCSTA)

• Baud Rate Control (BAUDCTL)

These are detailed in on the following pages in

and

respectively.

10.1

Clock Accuracy With

Asynchronous Operation

The factory calibrates the internal oscillator block out-

put (INTOSC) for 8 MHz. However, this frequency may

drift as VDD or temperature changes, and this directly

affects the asynchronous baud rate. Two methods may

be used to adjust the baud rate clock, but both require

a reference clock source of some kind.

The first (preferred) method uses the OSCTUNE

Adjusting the value in the OSCTUNE register allows for

fine resolution changes to the system clock source (see

Section 3.4

“Internal

Clock

Modes”

for

information).

The other method adjusts the value in the baud rate

generator. There may not be fine enough resolution

when adjusting the Baud Rate Generator to compensate

for a gradual change in the peripheral clock frequency.

Note:

The USART control will automatically

reconfigure the pin from input to output as

needed.

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