Microchip Technology AC244045 Data Sheet
PIC16F72X/PIC16LF72X
DS41341E-page 182
© 2009 Microchip Technology Inc.
17.2.6
TRANSMISSION
When the R/W bit of the received address byte is set
and an address match occurs, the R/W bit of the
SSPSTAT register is set and the slave will respond to
the master by reading out data. After the address match,
an ACK pulse is generated by the slave hardware and
the SCL pin is held low (clock is automatically stretched)
until the slave is ready to respond. See Section 17.2.7
“Clock Stretching”. The data the slave will transmit
must be loaded into the SSPBUF register, which sets
the BF bit. The SCL line is released by setting the CKP
bit of the SSPCON register.
and an address match occurs, the R/W bit of the
SSPSTAT register is set and the slave will respond to
the master by reading out data. After the address match,
an ACK pulse is generated by the slave hardware and
the SCL pin is held low (clock is automatically stretched)
until the slave is ready to respond. See Section 17.2.7
“Clock Stretching”. The data the slave will transmit
must be loaded into the SSPBUF register, which sets
the BF bit. The SCL line is released by setting the CKP
bit of the SSPCON register.
An SSP interrupt is generated for each transferred data
byte. The SSPIF flag bit of the PIR1 register initiates an
SSP interrupt, and must be cleared by software before
the next byte is transmitted. The BF bit of the SSPSTAT
register is cleared on the falling edge of the 8th
received clock pulse. The SSPIF flag bit is set on the
falling edge of the ninth clock pulse.
byte. The SSPIF flag bit of the PIR1 register initiates an
SSP interrupt, and must be cleared by software before
the next byte is transmitted. The BF bit of the SSPSTAT
register is cleared on the falling edge of the 8th
received clock pulse. The SSPIF flag bit is set on the
falling edge of the ninth clock pulse.
Following the 8th falling clock edge, control of the SDA
line is released back to the master so that the master
can acknowledge or not acknowledge the response. If
the master sends a not acknowledge, the slave’s
transmission is complete and the slave must monitor for
the next Start condition. If the master acknowledges,
control of the bus is returned to the slave to transmit
another byte of data. Just as with the previous byte, the
clock is stretched by the slave, data must be loaded into
the SSPBUF and CKP must be set to release the clock
line (SCL).
line is released back to the master so that the master
can acknowledge or not acknowledge the response. If
the master sends a not acknowledge, the slave’s
transmission is complete and the slave must monitor for
the next Start condition. If the master acknowledges,
control of the bus is returned to the slave to transmit
another byte of data. Just as with the previous byte, the
clock is stretched by the slave, data must be loaded into
the SSPBUF and CKP must be set to release the clock
line (SCL).
FIGURE 17-12:
I
2
C WAVEFORMS FOR TRANSMISSION (7-BIT ADDRESS)
SDA
SCL
SSPIF
BF
CKP
A7
A6
A5
A4
A3
A2
A1
ACK
D7
D6
D5
D4
D3
D2
D1
D0
ACK
Transmitting Data
R/W
Receiving Address
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
P
Cleared in software
Set bit after writing to SSPBUF
S
Data in
sampled
sampled
SCL held low
while CPU
while CPU
responds to SSPIF
(the SSPBUF must be written to
before the CKP bit can be set)
before the CKP bit can be set)
Dummy read of SSPBUF
to clear BF flag
SSPBUF is written in software
From SSP Interrupt
Service Routine