Datasheet

PIC16F882/883/884/886/887
DS41291F-page 198 © 2009 Microchip Technology Inc.
13.4.8 I
2
C™ MASTER MODE
TRANSMISSION
Transmission of a data byte, a 7-bit address, or the
other half of a 10-bit address, is accomplished by sim-
ply writing a value to the SSPBUF register. This action
will set the Buffer Full bit, BF, and allow the Baud Rate
Generator to begin counting and start the next trans-
mission. Each bit of address/data will be shifted out
onto the SDA pin after the falling edge of SCL is
asserted (see data hold time specification, parameter
106). SCL is held low for one Baud Rate Generator roll-
over count (T
BRG). Data should be valid before SCL is
released high (see data setup time specification,
parameter 107). When the SCL pin is released high, it
is held that way for T
BRG. The data on the SDA pin
must remain stable for that duration and some hold
time after the next falling edge of SCL. After the eighth
bit is shifted out (the falling edge of the eighth clock),
the BF bit is cleared and the master releases SDA,
allowing the slave device being addressed to respond
with an ACK
bit during the ninth bit time, if an address
match occurs, or if data was received properly. The
status of ACK is written into the ACKDT bit on the fall-
ing edge of the ninth clock. If the master receives an
Acknowledge, the Acknowledge Status bit, ACKSTAT,
is cleared. If not, the bit is set. After the ninth clock, the
SSPIF bit is set and the master clock (Baud Rate Gen-
erator) is suspended until the next data byte is loaded
into the SSPBUF, leaving SCL low and SDA
unchanged (Figure 13-15).
After the write to the SSPBUF, each bit of the address
will be shifted out on the falling edge of SCL, until all
seven address bits and the R/W
bit, are completed. On
the falling edge of the eighth clock, the master will de-
assert the SDA pin, allowing the slave to respond with
an Acknowledge. On the falling edge of the ninth clock,
the master will sample the SDA pin to see if the address
was recognized by a slave. The status of the ACK bit is
loaded into the ACKSTAT Status bit (SSPCON2 regis-
ter). Following the falling edge of the ninth clock trans-
mission of the address, the SSPIF is set, the BF bit is
cleared and the Baud Rate Generator is turned off, until
another write to the SSPBUF takes place, holding SCL
low and allowing SDA to float.
13.4.8.1 BF Status Flag
In Transmit mode, the BF bit (SSPSTAT register) is set
when the CPU writes to SSPBUF, and is cleared when
all eight bits are shifted out.
13.4.8.2 WCOL Status Flag
If the user writes the SSPBUF when a transmit is
already in progress (i.e., SSPSR is still shifting out a
data byte), the WCOL is set and the contents of the buf-
fer are unchanged (the write doesn’t occur). WCOL
must be cleared in software.
13.4.8.3 ACKSTAT Status Flag
In Transmit mode, the ACKSTAT bit (SSPCON2
register) is cleared when the slave has sent an
Acknowledge (ACK
= 0), and is set when the slave
does not Acknowledge (ACK
= 1). A slave sends an
Acknowledge when it has recognized its address
(including a general call), or when the slave has
properly received its data.
13.4.9 I
2
C™ MASTER MODE RECEPTION
Master mode reception is enabled by programming the
Receive Enable bit, RCEN (SSPCON2 register).
The Baud Rate Generator begins counting, and on
each rollover, the state of the SCL pin changes (high-
to-low/low-to-high) and data is shifted into the SSPSR.
After the falling edge of the eighth clock, the RCEN bit
is automatically cleared, the contents of the SSPSR are
loaded into the SSPBUF, the BF bit is set, the SSPIF
flag bit is set and the Baud Rate Generator is sus-
pended from counting, holding SCL low. The MSSP is
now in Idle state, awaiting the next command. When
the buffer is read by the CPU, the BF bit is automati-
cally cleared. The user can then send an Acknowledge
bit at the end of reception, by setting the Acknowledge
Sequence Enable bit ACKEN (SSPCON2 register).
13.4.9.1 BF Status Flag
In receive operation, the BF bit is set when an address
or data byte is loaded into SSPBUF from SSPSR. It is
cleared when the SSPBUF register is read.
13.4.9.2 SSPOV Status Flag
In receive operation, the SSPOV bit is set when eight
bits are received into the SSPSR and the BF bit is
already set from a previous reception.
13.4.9.3 WCOL Status Flag
If the user writes the SSPBUF when a receive is
already in progress (i.e., SSPSR is still shifting in a data
byte), the WCOL bit is set and the contents of the buffer
are unchanged (the write doesn’t occur).
Note: The MSSP module must be in an Idle state
before the RCEN bit is set, or the RCEN bit
will be disregarded.