Datasheet

PIC16C7X
DS30390E-page 96  1997 Microchip Technology Inc.
11.5.1.3 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 A
CK pulse will
be sent on the ninth bit, and pin RC3/SCK/SCL is held
low. The transmit data must be loaded into the SSP-
BUF register, which also loads the SSPSR register.
Then pin RC3/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 stretch-
ing 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 11-26).
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 A
CK pulse from the mas-
ter-receiver is latched on the rising edge of the ninth
SCL input pulse. If the SDA line was high (not A
CK),
then the data transfer is complete. When the A
CK 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 (A
CK), the transmit data must be loaded into
the SSPBUF register, which also loads the SSPSR reg-
ister. Then pin RC3/SCK/SCL should be enabled by
setting bit CKP.
FIGURE 11-26: 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
A
CKTransmitting 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
(the SSPBUF must be written-to
before the CKP bit can be set)
Applicable Devices
72 73 73A 74 74A 76 77