PIC17C752-08SLASHP datasheet(136/320 Pages) MICROCHIP

136 / 320 page

PIC17C75X

DS30264A-page 136

Preliminary

15.2.1.2

SLAVE RECEPTION

When the R/W bit of the address byte is clear and an

address match occurs, the R/W bit of the SSPSTAT

the SSPBUF register.

When the address byte overﬂow condition exists, then

no acknowledge (ACK) pulse is given. An overﬂow con-

dition is deﬁned as either bit BF (SSPSTAT<0>) is set

or bit SSPOV (SSPCON1<6>) is set.

An SSP interrupt is generated for each data transfer

byte. Flag bit SSPIF (PIR2<7>) must be cleared in soft-

ware. The SSPSTAT register is used to determine the

status of the byte.

Note: The SSPBUF will be loaded if the SSPOV

bit = 1 and the BF ﬂag = 0. If a read of the

SSPBUF was performed, but the user did

not clear the state of the SSPOV bit before

the next receive occured. The ACK is not

sent and the SSPBUF is updated.

15.2.1.3

SLAVE TRANSMISSION

When the R/W bit of the incoming address byte is set

and an address match occurs, the R/W bit of the

SSPSTAT register is set. The received address is

loaded into the SSPBUF register. The ACK pulse will

be sent on the ninth bit, and the SCLpin is held low. The

transmit data must be loaded into the SSPBUF register,

which also loads the SSPSR register. Then SCL pin

should be enabled by setting bit CKP (SSPCON1<4>).

The master must monitor the SCL pin prior to asserting

another clock pulse. The slave devices may be holding

off the master by stretching the clock. The eight data

bits are shifted out on the falling edge of the SCL input.

This ensures that the SDA signal is valid during the

SCL high time (Figure 15-16).

FIGURE 15-15: I2C WAVEFORMS FOR RECEPTION (7-BIT ADDRESS)

FIGURE 15-16: I2C WAVEFORMS FOR TRANSMISSION (7-BIT ADDRESS)

A7 A6 A5 A4 A3 A2 A1

SDA

SCL

Bus Master

terminates

transfer

Bit SSPOV is set because the SSPBUF register is still full.

Cleared in software

SSPBUF register is read

ACK

Receiving Data

ACK

R/W=0

Receiving Address

SSPIF (PIR2<7>)

BF (SSPSTAT<0>)

SSPOV (SSPCON1<6>)

ACK

ACK is not sent.

SDA

SCL

SSPIF (PIR1<3>)

BF (SSPSTAT<0>)

CKP (SSPCON1<4>)

ACK

Transmitting Data

R/W = 1

Receiving Address

56789

123

cleared in software

SSPBUF is written in software

From SSP interrupt

service routine

Set bit after writing to SSPBUF

Data in

sampled

SCL held low

while CPU

responds to SSPIF

(the SSPBUF must be written-to

before the CKP bit can be set)

PIC17C752-08/P Datasheet(PDF) 136 Page - Microchip Technology

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