PIC16F1825T-ESS datasheet(246/448 Pages) MICROCHIP

246 / 448 page

PIC16(L)F1825/1829

DS41440C-page 246

 2010-2012 Microchip Technology Inc.

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

eight 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

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.

The SSPxSR is not directly readable or writable and

can only be accessed by addressing the SSPxBUF

the various Status conditions.

FIGURE 25-5:

SPI MASTER/SLAVE CONNECTION

Serial Input Buffer

(BUF)

Shift Register

(SSPxSR)

MSb

LSb

SDOx

SDIx

Processor 1

SCKx

SPI Master SSPM<3:0> = 00xx

Serial Input Buffer

(SSPxBUF)

Shift Register

(SSPxSR)

LSb

MSb

SDIx

SDOx

Processor 2

SCKx

SPI Slave SSPM<3:0> = 010x

Serial Clock

SSx

Slave Select

General I/O

(optional)

= 1010

PIC16F1825T-ESS Datasheet(PDF) 246 Page - Microchip Technology

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