PIC16F720-ESLASHML datasheet(124/244 Pages) MICROCHIP

124 / 244 page

PIC16F/LF720/721

DS41430A-page 124

 2010 Microchip Technology Inc.

16.1.2.2

Receiving Data

The receiver data recovery circuit initiates character

reception on the falling edge of the first bit. The first bit,

also known as the Start bit, is always a zero. The data

recovery circuit counts one-half bit time to the center of

the Start bit and verifies that the bit is still a zero. If it is

not a zero then the data recovery circuit aborts

character reception, without generating an error, and

resumes looking for the falling edge of the Start bit. If

the Start bit zero verification succeeds then the data

recovery circuit counts a full bit time to the center of the

next bit. The bit is then sampled by a majority detect

circuit and the resulting ‘0’ or ‘1’ is shifted into the RSR.

This repeats until all data bits have been sampled and

shifted into the RSR. One final bit time is measured and

the level sampled. This is the Stop bit, which is always

a ‘1’. If the data recovery circuit samples a ‘0’ in the

Stop bit position then a framing error is set for this

character, otherwise the framing error is cleared for this

character.

Refer

Section 16.1.2.4

“Receive

Framing Error” for more information on framing

errors.

Immediately after all data bits and the Stop bit have

been received, the character in the RSR is transferred

to the AUSART receive FIFO and the RCIF interrupt

flag bit of the PIR1 register is set. The top character in

the FIFO is transferred out of the FIFO by reading the

RCREG register.

16.1.2.3

Receive Interrupts

The RCIF interrupt flag bit of the PIR1 register is set

whenever the AUSART receiver is enabled and there is

an unread character in the receive FIFO. The RCIF

interrupt flag bit is read-only, it cannot be set or cleared

by software.

RCIF interrupts are enabled by setting all of the

following bits:

• RCIE interrupt enable bit of the PIE1 register

• PEIE, Peripheral Interrupt Enable bit of the

INTCON register

• GIE, Global Interrupt Enable bit of the INTCON

The RCIF interrupt flag bit of the PIR1 register will be

set when there is an unread character in the FIFO,

regardless of the state of interrupt enable bits.

16.1.2.4

Receive Framing Error

Each character in the receive FIFO buffer has a

corresponding framing error Status bit. A framing error

indicates that a Stop bit was not seen at the expected

time. The framing error status is accessed via the

FERR bit of the RCSTA register. The FERR bit

represents the status of the top unread character in the

receive FIFO. Therefore, the FERR bit must be read

before reading the RCREG.

The FERR bit is read-only and only applies to the top

unread character in the receive FIFO. A framing error

(FERR = 1) does not preclude reception of additional

characters. It is not necessary to clear the FERR bit.

Reading the next character from the FIFO buffer will

advance the FIFO to the next character and the next

corresponding framing error.

The FERR bit can be forced clear by clearing the SPEN

bit of the RCSTA register which resets the AUSART.

Clearing the CREN bit of the RCSTA register does not

affect the FERR bit. A framing error by itself does not

generate an interrupt.

16.1.2.5

Receive Overrun Error

The receive FIFO buffer can hold two characters. An

overrun error will be generated if a third character, in its

entirety, is received before the FIFO is accessed. When

this happens the OERR bit of the RCSTA register is set.

The characters already in the FIFO buffer can be read

but no additional characters will be received until the

error is cleared. The error must be cleared by either

clearing the CREN bit of the RCSTA register or by

setting the AUSART by clearing the SPEN bit of the

RCSTA register.

16.1.2.6

Receiving 9-bit Characters

The AUSART supports 9-bit character reception. When

the RX9 bit of the RCSTA register is set, the AUSART

will shift 9 bits into the RSR for each character

received. The RX9D bit of the RCSTA register is the

ninth and Most Significant data bit of the top unread

character in the receive FIFO. When reading 9-bit data

from the receive FIFO buffer, the RX9D data bit must

be read before reading the 8 Least Significant bits from

the RCREG.

Note:

If the receive FIFO is overrun, no additional

characters will be received until the overrun

condition

cleared.

Refer

Section 16.1.2.5

“Receive

Overrun

Error” for more information on overrun

errors.

Note:

If all receive characters in the receive

FIFO have framing errors, repeated reads

of the RCREG will not clear the FERR bit.

PIC16F720-E/ML Datasheet(PDF) 124 Page - Microchip Technology

PIC16F720-E/ML Datasheet(HTML) 124 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Descarga

Enlace URL