Microchip Technology MA160014 Data Sheet

DS41412F-page 244

 2010-2012 Microchip Technology Inc.

15.6.4 I

2

C MASTER MODE START 

CONDITION TIMING

To initiate a Start condition (

), the user

sets the Start Enable bit, SEN, of the SSPxCON2 reg-
ister. If the SDAx and SCLx pins are sampled high, the
Baud Rate Generator is reloaded with the contents of
SSPxADD<7:0> and starts its count. If SCLx and
SDAx are both sampled high when the Baud Rate
Generator times out (T

BRG

), the SDAx pin is driven

low. The action of the SDAx being driven low while
SCLx is high is the Start condition and causes the S bit
of the SSPxSTAT1 register to be set. Following this,
the Baud Rate Generator is reloaded with the contents
of SSPxADD<7:0> and resumes its count. When the
Baud Rate Generator times out (T

BRG

), the SEN bit of

the SSPxCON2 register will be automatically cleared

by hardware; the Baud Rate Generator is suspended,
leaving the SDAx line held low and the Start condition
is complete.

Note 1: If at the beginning of the Start condition,

the SDAx and SCLx pins are already sam-
pled low, or if during the Start condition,
the SCLx line is sampled low before the
SDAx line is driven low, a bus collision
occurs, the Bus Collision Interrupt Flag,
BCLxIF, 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.

SDAx

SCLx

S

T

BRG

1st bit

2nd bit

T

BRG

SDAx = 1, 

At completion of Start bit,

SCLx = 1

Write to SSPxBUF occurs here

T

BRG

hardware clears SEN bit

T

BRG

Write to SEN bit occurs here

Set S bit (SSPxSTAT<3>)

    and sets SSPxIF bit