PIC16F946 Datasheet, PDF (181/274 Pages) Microchip Technology – 64-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt Technology

PIC16F946
14.12.3 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
RC6/TX/CK/SCK/SCL/SEG9 is held low. The transmit
data must be loaded into the SSPBUF register, which
also loads the SSPSR register. Then, pin
RC6/TX/CK/SCK/SCL/SEG9 should be enabled by
setting bit CKP (SSPCON<4>). The master must mon-
itor 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 14-10).
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 occur-
rence 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
RC6/TX/CK/SCK/SCL/SEG9 should be enabled by
setting bit CKP.
FIGURE 14-10: 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)
© 2005 Microchip Technology Inc.
Preliminary
DS41265A-page 179