2003 Microchip Technology Inc.
DS39582B-page 85
PIC16F87XA
9.4.3.2
Reception
When the R/W bit of the address byte is clear and an
address match occurs, the R/W bit of the SSPSTAT
register is cleared. The received address is loaded into
the SSPBUF register and the SDA line is held low
(ACK).
When the address byte overflow condition exists, then
the No Acknowledge (ACK) pulse is given. An overflow
condition is defined as either bit BF (SSPSTAT<0>) is
set or bit SSPOV (SSPCON<6>) is set.
An MSSP interrupt is generated for each data transfer
byte. Flag bit SSPIF (PIR1<3>) must be cleared in soft-
ware. The SSPSTAT register is used to determine the
status of the byte.
If SEN is enabled (SSPCON<0> =
1
), RC3/SCK/SCL
will be held low (clock stretch) following each data trans-
fer. The clock must be released by setting bit CKP
(SSPCON<4>). See Section 9.4.4 “Clock Stretching”
for more detail.
9.4.3.3
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 regard-
less of SEN (see Section 9.4.4 “Clock Stretching” for
more detail). By stretching the clock, the master will be
unable to assert another clock pulse until the slave is
done preparing the transmit data. The transmit data
must be loaded into the SSPBUF register, which also
loads the SSPSR register. Then pin RC3/SCK/SCL
should be enabled by setting bit CKP (SSPCON<4>).
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 9-9).
The ACK pulse from the master-receiver is latched on
the rising edge of the ninth SCL input pulse. If the SDA
line is high (not ACK), then the data transfer is com-
plete. In this case, when the ACK is latched by the
slave, the slave logic is reset (resets SSPSTAT regis-
ter) and the slave monitors for another occurrence of
the Start bit. If the SDA line was low (ACK), the next
transmit data must be loaded into the SSPBUF register.
Again, pin RC3/SCK/SCL must be enabled by setting
bit CKP.
An MSSP interrupt is generated for each data transfer
byte. The SSPIF bit must be cleared in software and
the SSPSTAT register is used to determine the status
of the byte. The SSPIF bit is set on the falling edge of
the ninth clock pulse.
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