PIC16F631_08 Datasheet, PDF (195/306 Pages) Microchip Technology – 20-Pin Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology

PIC16F631/677/685/687/689/690
13.12.4 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 RB6/SCK/SCL is held
low. The transmit data must be loaded into the
SSPBUF register, which also loads the SSPSR
register. Then, pin RB6/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 13-10).
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 (resets SSPSTAT
register) 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 RB6/SCK/SCL should be enabled by
setting bit CKP.
FIGURE 13-10: I²C™ WAVEFORMS FOR TRANSMISSION (7-BIT ADDRESS)
SDA
Receiving Address
R/W = 1
A7 A6 A5 A4 A3 A2 A1
ACK
Transmitting Data ACK
D7 D6 D5 D4 D3 D2 D1 D0
SCL
S
1 23456789
1234 56789
Data in
SCL held low
P
sampled
while CPU
responds to SSPIF
SSPIF (PIR1<3>)
Cleared in software
BF (SSPSTAT<0>)
From SSP Interrupt
SSPBUF is written in software Service Routine
CKP (SSPCON<4>)
Set bit after writing to SSPBUF
(the SSPBUF must be written to
before the CKP bit can be set)
© 2008 Microchip Technology Inc.
DS41262E-page 193