PIC16F631 datasheet(173/294 Pages) MICROCHIP

173 / 294 page

DS41262D-page 171

PIC16F631/677/685/687/689/690

12.4.1.5

Synchronous Master Reception

Data is received at the RX/DT pin. The RX/DT and

TX/CK pin output drivers are automatically disabled

when the EUSART is configured for synchronous

master receive operation.

In Synchronous mode, reception is enabled by setting

either the Single Receive Enable bit (SREN of the

RCSTA register) or the Continuous Receive Enable bit

(CREN of the RCSTA register).

When SREN is set and CREN is clear, only as many

clock cycles are generated as there are data bits in a

single character. The SREN bit is automatically cleared

at the completion of one character. When CREN is set,

clocks are continuously generated until CREN is

cleared. If CREN is cleared in the middle of a character

the CK clock stops immediately and the partial charac-

ter is discarded. If SREN and CREN are both set, then

SREN is cleared at the completion of the first character

and CREN takes precedence.

To initiate reception, set either SREN or CREN. Data is

sampled at the RX/DT pin on the trailing edge of the

TX/CK clock pin and is shifted into the Receive Shift

received into the RSR, the RCIF bit is set and the char-

acter is automatically transferred to the two character

receive FIFO. The Least Significant eight bits of the top

character in the receive FIFO are available in RCREG.

The RCIF bit remains set as long as there are un-read

characters in the receive FIFO.

12.4.1.6

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 RCREG is read to access

the FIFO. When this happens the OERR bit of the

RCSTA register is set. Previous data in the FIFO will

not be overwritten. The two characters in the FIFO

buffer can be read, however, no additional characters

will be received until the error is cleared. The OERR bit

can only be cleared by clearing the overrun condition.

If the overrun error occurred when the SREN bit is set

and CREN is clear then the error is cleared by reading

RCREG. If the overrun occurred when the CREN bit is

set then the error condition is cleared by either clearing

the CREN bit of the RCSTA register or by clearing the

SPEN bit which resets the EUSART.

12.4.1.7

Receiving 9-bit Characters

The EUSART supports 9-bit character reception. When

the RX9 bit of the RCSTA register is set the EUSART

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.

12.4.1.8

Synchronous Master Reception

Set-up:

Initialize the SPBRGH, SPBRG register pair for

the appropriate baud rate. Set or clear the

BRGH and BRG16 bits, as required, to achieve

the desired baud rate.

Enable the synchronous master serial port by

setting bits SYNC, SPEN and CSRC.

Ensure bits CREN and SREN are clear.

If using interrupts, set the GIE and PEIE bits of

the INTCON register and set RCIE.

If 9-bit reception is desired, set bit RX9.

Start reception by setting the SREN bit or for

continuous reception, set the CREN bit.

Interrupt flag bit RCIF will be set when reception

of a character is complete. An interrupt will be

generated if the enable bit RCIE was set.

Read the RCSTA register to get the ninth bit (if

enabled) and determine if any error occurred

during reception.

Read the 8-bit received data by reading the

RCREG register.

10. If an overrun error occurs, clear the error by

either clearing the CREN bit of the RCSTA

the EUSART.

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