PIC18F45J10 FAMILY
16.4.10 I2C MASTER MODE
TRANSMISSION
The user should verify that the WCOL is clear after
each write to SSPxBUF to ensure the transfer is
correct. In all cases, WCOL must be cleared in
software.
Transmission of a data byte, a 7-bit address or the
other half of a 10-bit address is accomplished by simply
writing a value to the SSPxBUF register. This action will
set the Buffer Full flag 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 SDAx pin after the falling edge of SCLx is
asserted (see data hold time specification
parameter 106). SCLx is held low for one Baud Rate
Generator rollover count (TBRG). Data should be valid
before SCLx is released high (see data setup time
specification parameter 107). When the SCLx pin is
released high, it is held that way for TBRG. The data on
the SDAx pin must remain stable for that duration and
some hold time after the next falling edge of SCLx.
After the eighth bit is shifted out (the falling edge of the
eighth clock), the BF flag is cleared and the master
releases SDAx. This allows the slave device being
addressed to respond with an ACK bit during the ninth
bit time if an address match occurred, or if data was
received properly. The status of ACK is written into the
ACKDT bit on the falling 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 SSPxIF bit is set and the
master clock (Baud Rate Generator) is suspended until
the next data byte is loaded into the SSPxBUF, leaving
SCLx low and SDAx unchanged (Figure 16-21).
16.4.10.3 ACKSTAT Status Flag
In Transmit mode, the ACKSTAT bit (SSPxCON2<6>)
is cleared when the slave has sent an Acknowledge
(ACK = 0) and is set when the slave does not Acknowl-
edge (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.
16.4.11 I2C MASTER MODE RECEPTION
Master mode reception is enabled by programming the
Receive Enable bit, RCEN (SSPxCON2<3>).
Note:
The MSSP module must be in an Idle state
before the RCEN bit is set or the RCEN bit
will be disregarded.
The Baud Rate Generator begins counting, and on
each rollover, the state of the SCLx pin changes
(high-to-low/low-to-high) and data is shifted into the
SSPxSR. After the falling edge of the eighth clock, the
receive enable flag is automatically cleared, the con-
tents of the SSPxSR are loaded into the SSPxBUF, the
BF flag bit is set, the SSPxIF flag bit is set and the Baud
Rate Generator is suspended from counting, holding
SCLx low. The MSSP is now in Idle state awaiting the
next command. When the buffer is read by the CPU,
the BF flag bit is automatically cleared. The user can
then send an Acknowledge bit at the end of reception
by setting the Acknowledge Sequence Enable bit,
ACKEN (SSPxCON2<4>).
After the write to the SSPxBUF, each bit of the address
will be shifted out on the falling edge of SCLx until all
seven address bits and the R/W bit are completed. On
the falling edge of the eighth clock, the master will
deassert the SDAx pin, allowing the slave to respond
with an Acknowledge. On the falling edge of the ninth
clock, the master will sample the SDAx pin to see if the
address was recognized by a slave. The status of the
ACK bit is loaded into the ACKSTAT status bit
(SSPxCON2<6>). Following the falling edge of the
ninth clock transmission of the address, the SSPxIF is
set, the BF flag is cleared and the Baud Rate Generator
is turned off until another write to the SSPxBUF takes
place, holding SCLx low and allowing SDAx to float.
16.4.11.1 BF Status Flag
In receive operation, the BF bit is set when an address
or data byte is loaded into SSPxBUF from SSPxSR. It
is cleared when the SSPxBUF register is read.
16.4.11.2 SSPOV Status Flag
In receive operation, the SSPOV bit is set when 8 bits
are received into the SSPxSR and the BF flag bit is
already set from a previous reception.
16.4.10.1 BF Status Flag
16.4.11.3 WCOL Status Flag
In Transmit mode, the BF bit (SSPxSTAT<0>) is set
when the CPU writes to SSPxBUF and is cleared when
all 8 bits are shifted out.
If the user writes the SSPxBUF when a receive is
already in progress (i.e., SSPxSR 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).
16.4.10.2 WCOL Status Flag
If the user writes to the SSPxBUF when a transmit is
already in progress (i.e., SSPxSR 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) after 2 TCY
after the SSPxBUF write. If SSPxBUF is rewritten
within 2 TCY, the WCOL bit is set and SSPxBUF is
updated. This may result in a corrupted transfer.
DS39682E-page 182
© 2009 Microchip Technology Inc.
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