PIC16 datasheet(215/418 Pages) MICROCHIP

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DS40001609C-page 215

PIC16(L)F1508/9

21.6.4

C MASTER MODE START

CONDITION TIMING

To initiate a Start condition (Figure 21-26), the user

sets the Start Enable bit, SEN bit of the SSPxCON2

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 (TBRG), 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 (TBRG), 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.

FIGURE 21-26:

FIRST START BIT TIMING

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 I2C module is reset into

its Idle state.

2: The Philips I2C Specification states that a

bus collision cannot occur on a Start.

SDAx

SCLx

TBRG

1st bit

2nd bit

TBRG

SDAx = 1,

At completion of Start bit,

SCLx = 1

Write to SSPxBUF occurs here

TBRG

hardware clears SEN bit

TBRG

Write to SEN bit occurs here

Set S bit (SSPxSTAT<3>)

and sets SSPxIF bit

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