PIC16F818/819
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.
the data transfer is complete. When the ACK is latched
by the slave device, the slave logic is reset (resets
SSPSTAT register) and the slave device 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 RB4/SCK/SCL should be enabled by
setting bit, CKP.
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
TABLE 10-2: DATA TRANSFER RECEIVED BYTE ACTIONS
Status Bits as Data
Transfer is Received
Set bit SSPIF
(SSP interrupt occurs if enabled)
SSPSR → SSPBUF
Generate ACK Pulse
BF
SSPOV
0
1
1
0
0
0
1
1
Yes
No
No
No
Yes
No
No
No
Yes
Yes
Yes
Yes
Note 1: Shaded cells show the conditions where the user software did not properly clear the overflow condition.
FIGURE 10-6:
I2C™ WAVEFORMS FOR RECEPTION (7-BIT ADDRESS)
Receiving Address
R/W = 0
Receiving Data
Receiving Data
ACK
9
ACK
9
ACK
9
A7 A6 A5 A4
SDA
SCL
A3 A2 A1
D2
D0
8
D5
D2
D0
8
D5 D4 D3
D7 D6
D1
7
D7 D6
D4 D3
D1
7
3
7
1
2
4
5
3
6
5
6
1
2
3
6
1
2
4
8
4
5
P
S
SSPIF (PIR1<3>)
BF (SSPSTAT<0>)
Cleared in software
Bus master
terminates
transfer
SSPBUF register is read
SSPOV (SSPCON<6>)
Bit SSPOV is set because the SSPBUF register is still full
ACK is not sent
FIGURE 10-7:
I2C™ WAVEFORMS FOR TRANSMISSION (7-BIT ADDRESS)
Receiving Address
A7 A6 A5 A4 A3 A2 A1
R/W = 1
ACK
Transmitting Data
ACK
SDA
SCL
D7 D6 D5 D4 D3 D2 D1 D0
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
S
P
SCL held low
while CPU
responds to SSPIF
Data is
Sampled
SSPIF (PIR1<3>)
BF (SSPSTAT<0>)
Cleared in software
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)
DS39598E-page 78
2004 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
