PIC18F23K22-ESLASHML datasheet(212/496 Pages) MICROCHIP

212 / 496 page

PIC18(L)F2X/4XK22

DS41412C-page 212

Preliminary

 2010 Microchip Technology Inc.

Any serial port function that is not desired may be

overridden by programming the corresponding data

direction (TRIS) register to the opposite value.

The MSSPx consists of a transmit/receive shift register

(SSPxSR) and a buffer register (SSPxBUF). The

SSPxSR shifts the data in and out of the device, MSb

first. The SSPxBUF holds the data that was written to

the SSPxSR until the received data is ready. Once the

8 bits of data have been received, that byte is moved to

the SSPxBUF register. Then, the Buffer Full Detect bit,

BF of the SSPxSTAT register, and the interrupt flag bit,

SSPxIF, are set. This double-buffering of the received

data (SSPxBUF) allows the next byte to start reception

before reading the data that was just received. Any

write to the SSPxBUF register during transmission/

reception of data will be ignored and the write collision

detect bit, WCOL of the SSPxCON1 register, will be

set. User software must clear the WCOL bit to allow the

following write(s) to the SSPxBUF register to complete

successfully.

When the application software is expecting to receive

valid data, the SSPxBUF should be read before the

next byte of data to transfer is written to the SSPxBUF.

The Buffer Full bit, BF of the SSPxSTAT register,

indicates when SSPxBUF has been loaded with the

received data (transmission is complete). When the

SSPxBUF is read, the BF bit is cleared. This data may

be irrelevant if the SPI is only a transmitter. Generally,

the MSSPx interrupt is used to determine when the

transmission/reception has completed. If the interrupt

method is not going to be used, then software polling

can be done to ensure that a write collision does not

occur.

FIGURE 15-5:

SPI MASTER/SLAVE CONNECTION

Serial Input Buffer

(BUF)

Shift Register

(SSPxSR)

MSb

LSb

SDOx

SDIx

Processor 1

SCKx

SPI Master SSPxM<3:0> = 00xx

Serial Input Buffer

(SSPxBUF)

Shift Register

(SSPxSR)

LSb

MSb

SDIx

SDOx

Processor 2

SCKx

SPI Slave SSPxM<3:0> = 010x

Serial Clock

SSx

Slave Select

General I/O

(optional)

= 1010

PIC18F23K22-E/ML Datasheet(PDF) 212 Page - Microchip Technology

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