PIC18F4539T-I/ML【PDF 48/322 页】IC MCU FLASH 12KX16 EE A/D 44QFN

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2002 Microchip Technology Inc.

Preliminary

DS30485A-page 139

PIC18FXX39

16.4.3.2

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 and the SDA line is held low

(ACK).

When the address byte overflow condition exists, then

the no Acknowledge (ACK) pulse is given. An overflow

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

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

An MSSP interrupt is generated for each data transfer

byte. Flag bit SSPIF (PIR1<3>) must be cleared in soft-

ware. The SSPSTAT register is used to determine the

status of the byte.

If SEN is enabled (SSPCON1<0> = 1), RC3/SCK/SCL

will be held low (clock stretch) following each data trans-

fer. The clock must be released by setting bit CKP

(SSPCON<4>). See Section 16.4.4 (“Clock Stretching”),

for more detail.

16.4.3.3

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 pin RC3/SCK/SCL is held

low, regardless of SEN (see “Clock Stretching”,

Section 16.4.4, for more detail). By stretching the clock,

the master will be unable to assert another clock pulse

until the slave is done preparing the transmit data. The

transmit data must be loaded into the SSPBUF register,

which also loads the SSPSR register. Then, pin RC3/

SCK/SCL should be enabled by setting bit CKP

(SSPCON1<4>). 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 16-9).

The ACK pulse from the master-receiver is latched on

the rising edge of the ninth SCL input pulse. If the SDA

line is high (not ACK), then the data transfer is com-

plete. In this case, when the ACK is latched by the

slave, the slave logic is reset (resets SSPSTAT regis-

ter) and the slave monitors for another occurrence of

the START bit. If the SDA line was low (ACK), the next

transmit data must be loaded into the SSPBUF register.

Again, pin RC3/SCK/SCL must be enabled by setting

bit CKP.

An MSSP interrupt is generated for each data transfer

byte. The SSPIF bit must be cleared in software and

the SSPSTAT register is used to determine the status

of the byte. The SSPIF bit is set on the falling edge of

the ninth clock pulse.

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