PIC16C63A/65B/73B/74B
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.
10.3.1.3
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 10-7).
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 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 reg-
ister. Then pin RC3/SCK/SCL should be enabled by
setting bit CKP.
FIGURE 10-7:
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)
2000 Microchip Technology Inc.
DS30605C-page 63
MICROCHIP [ MICROCHIP ]
