Datasheet
2010 Microchip Technology Inc. DS39616D-page 215
PIC18F2331/2431/4331/4431
19.3.1.3 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, SCK/SCL, is held low.
The transmit data must be loaded into the SSPBUF
register, which also loads the SSPSR register. Then,
pin, SCK/SCL, should be enabled by setting bit, CKP
(SSPCON<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 19-7).
An SSP interrupt is generated for each data transfer
byte. Flag bit, SSPIF, must be cleared in software and
the SSPSTAT register is used to determine the status
of the byte. Flag bit, SSPIF, is set on the falling edge of
the ninth clock pulse.
As a slave-transmitter, the ACK
pulse from the master-
receiver is latched on the rising edge of the ninth SCL
input pulse. If the SDA line was high (not ACK), then the
data transfer is complete. When the ACK
is latched by
the slave, the slave logic is reset and the slave then
monitors for another occurrence of the Start bit. If the
SDA line was low (ACK
), the transmit data must be
loaded into the SSPBUF register, which also loads the
SSPSR register. Then pin, SCK/SCL, should be enabled
by setting bit CKP.
FIGURE 19-7: I
2
C™ WAVEFORMS FOR TRANSMISSION (7-BIT ADDRESS)
SDA
SCL
SSPIF (PIR1<3>)
BF (SSPSTAT<0>)
CKP (SSPCON<4>)
A7 A6 A5 A4 A3 A2 A1 ACK
D7 D6 D5 D4 D3 D2 D1 D0
ACK
Transmitting DataR/W = 1Receiving Address
123456789 123456789
P
Cleared in software
SSPBUF is written in software
From SSP Interrupt
Service Routine
Set bit after writing to SSPBUF
S
Data in
sampled
SCL held low
while CPU
responds to SSPIF
(SSPBUF must be written to
before the CKP bit can be set)