PIC16F7X
FIGURE 9-6:
I2C WAVEFORMS FOR RECEPTION (7-BIT ADDRESS)
R/W=0
Receiving Address
A7 A6 A5 A4
Receiving Data
Receiving Data
ACK
9
ACK
9
ACK
9
SDA
SCL
A3 A2 A1
D7 D6 D5 D4 D3 D2
D0
8
D7 D6
D5
D4 D3
D2
D0
8
D1
7
D1
7
3
7
1
2
4
5
4
3
6
5
6
1
2
3
6
1
2
4
8
5
P
S
SSPIF (PIR1<3>)
Cleared in software
Bus Master
terminates
transfer
BF (SSPSTAT<0>)
SSPBUF register is read
SSPOV (SSPCON<6>)
Bit SSPOV is set because the SSPBUF register is still full.
ACK is not sent.
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.
9.3.1.3
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 RC3/SCK/SCL is held
low. The transmit data must be loaded into the
SSPBUF register, which also loads the SSPSR regis-
ter. Then, pin RC3/SCK/SCL should be enabled by set-
ting 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 9-7).
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 reg-
ister, which also loads the SSPSR register. Then pin
RC3/SCK/SCL should be enabled by setting bit CKP.
FIGURE 9-7:
I2C WAVEFORMS FOR TRANSMISSION (7-BIT ADDRESS)
Receiving Address
R/W = 1
ACK
Transmitting Data
ACK
9
SDA
A7 A6 A5 A4 A3 A2 A1
D7 D6 D5 D4 D3 D2 D1 D0
SCL
S
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
P
SCL held low
while CPU
responds to SSPIF
Data in
sampled
Cleared in software
SSPIF (PIR1<3>)
BF (SSPSTAT<0>)
From SSP Interrupt
Service Routine
SSPBUF is written in software
CKP (SSPCON<4>)
Set bit after writing to SSPBUF
(the SSPBUF must be written to
before the CKP bit can be set)
2002 Microchip Technology Inc.
DS30325B-page 67
MICROCHIP [ MICROCHIP ]
