16F1829 datasheet(306/420 Pages) MICROCHIP

306 / 420 page

PIC16F/LF1825/1829

DS41440A-page 308

Preliminary

 2010 Microchip Technology Inc.

26.2

Clock Accuracy with

Asynchronous Operation

The factory calibrates the internal oscillator block out-

put (INTOSC). However, the INTOSC 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

value in the OSCTUNE register allows for fine resolution

changes to the system clock source. See Section 6.2.2

“Internal Clock Sources” for more information.

The other method adjusts the value in the Baud Rate

Generator. This can be done automatically with the

Auto-Baud

Detect

feature

(see

Section 27.3.1

“Auto-Baud Detect”). There may not be fine enough

resolution when adjusting the Baud Rate Generator to

compensate for a gradual change in the peripheral

clock frequency.

TXSTA: TRANSMIT STATUS AND CONTROL REGISTER

R/W-/0

R/W-0/0

R-1/1

R/W-0/0

CSRC

TX9

TXEN(1)

SYNC

SENDB

BRGH

TRMT

TX9D

bit 7

bit 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

u = Bit is unchanged

x = Bit is unknown

-n/n = Value at POR and BOR/Value at all other Resets

‘1’ = Bit is set

‘0’ = Bit is cleared

bit 7

CSRC: Clock Source Select bit

Asynchronous mode:

Don’t care

Synchronous mode:

1 = Master mode (clock generated internally from BRG)

0 = Slave mode (clock from external source)

bit 6

TX9: 9-bit Transmit Enable bit

1 = Selects 9-bit transmission

0 = Selects 8-bit transmission

bit 5

TXEN: Transmit Enable bit(1)

1 = Transmit enabled

0 = Transmit disabled

bit 4

SYNC: EUSART Mode Select bit

1 = Synchronous mode

0 = Asynchronous mode

bit 3

SENDB: Send Break Character bit

Asynchronous mode:

1 = Send Sync Break on next transmission (cleared by hardware upon completion)

0 = Sync Break transmission completed

Synchronous mode:

Don’t care

bit 2

BRGH: High Baud Rate Select bit

Asynchronous mode:

1 = High speed

0 = Low speed

Synchronous mode:

Unused in this mode

bit 1

TRMT: Transmit Shift Register Status bit

1 = TSR empty

0 = TSR full

bit 0

TX9D: Ninth bit of Transmit Data

Can be address/data bit or a parity bit.

Note 1:

SREN/CREN overrides TXEN in Sync mode.

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