Datasheet

 2011-2012 Microchip Technology Inc. DS41441C-page 235
PIC12(L)F1840
25.6.4 I
2
C MASTER MODE START
CONDITION TIMING
To initiate a Start condition (Figure 25-26), the user
sets the Start Enable bit, SEN bit of the SSP1CON2
register. If the SDA and SCL pins are sampled high,
the Baud Rate Generator is reloaded with the contents
of SSP1ADD<7:0> 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
SSP1STAT1 register to be set. Following this, the
Baud Rate Generator is reloaded with the contents of
SSP1ADD<7:0> and resumes its count. When the
Baud Rate Generator times out (T
BRG), the SEN bit of
the SSP1CON2 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.
FIGURE 25-26: FIRST START BIT TIMING
Note 1: 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,
BCL1IF, is set, the Start condition is
aborted and the I
2
C module is reset into
its Idle state.
2: The Philips I
2
C Specification states that a
bus collision cannot occur on a Start.
SDA
SCL
S
TBRG
1st bit
2nd bit
TBRG
SDA = 1,
At completion of Start bit,
SCL = 1
Write to SSP1BUF occurs here
TBRG
hardware clears SEN bit
TBRG
Write to SEN bit occurs here
Set S bit (SSP1STAT<3>)
and sets SSP1IF bit