Datasheet

PIC18F2XK20/4XK20
DS40001303H-page 210  2010-2015 Microchip Technology Inc.
17.4.8 I
2
C MASTER MODE START
CONDITION TIMING
To initiate a Start condition, the user sets the Start
Enable bit, SEN bit of the SSPCON2 register. If the
SDA and SCL pins are sampled high, the Baud Rate
Generator is reloaded with the contents of
SSPADD<6:0> and starts its count. If SCL and SDA are
both sampled high when the Baud Rate Generator
times out (T
BRG), the SDA pin is driven low. The action
of the SDA being driven low while SCL is high is the
Start condition and causes the S bit of the SSPSTAT1
register to be set. Following this, the Baud Rate Gener-
ator is reloaded with the contents of SSPADD<7:0>
and resumes its count. When the Baud Rate Generator
times out (T
BRG), the SEN bit of the SSPCON2 register
will be automatically cleared by hardware; the Baud
Rate Generator is suspended, leaving the SDA line
held low and the Start condition is complete.
17.4.8.1 WCOL Status Flag
If the user writes the SSPBUF when a Start sequence
is in progress, the WCOL is set and the contents of the
buffer are unchanged (the write does not occur).
FIGURE 17-19: FIRST START BIT TIMING
Note: If at the beginning of the Start condition,
the SDA and SCL pins are already sam-
pled low, or if during the Start condition,
the SCL line is sampled low before the
SDA line is driven low, a bus collision
occurs, the Bus Collision Interrupt Flag,
BCLIF, is set, the Start condition is aborted
and the I
2
C module is reset into its Idle
state.
Note: Because queuing of events is not allowed,
writing to the lower five bits of SSPCON2
is disabled until the Start condition is
complete.
SDA
SCL
S
TBRG
1st bit
2nd bit
TBRG
SDA = 1,
At completion of Start bit,
SCL = 1
Write to SSPBUF occurs here
TBRG
hardware clears SEN bit
TBRG
Write to SEN bit occurs here
Set S bit (SSPSTAT<3>)
and sets SSPIF bit