PIC17C752-08SLASHP datasheet(144/320 Pages) MICROCHIP

144 / 320 page

PIC17C75X

DS30264A-page 144

Preliminary

15.2.7

I2C MASTER MODE START CONDITION

TIMING

To initiate a START condition the user sets the start

condition enable bit or SEN bit (SSPCON2<0>). If the

SDA and SCL pins are sampled high, the baud rate

generator

re-loaded

with

the

contents

SSPADD<6:0>, and starts its count. If SCL and SDA

are both sampled high when the baud rate generator

times out (TBRG), 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 (SSPSTAT<3>)

to be set. Since the I2C module is conﬁgured in master

mode, a '1' in the S bit causes the SSPIF ﬂag to be

set. Following this, the baud rate generator is reloaded

with the contents of SSPADD<6:0> and resumes its

count. When the baud rate generator times out (TBRG)

the SEN bit in the SSPCON2 register will be automati-

cally cleared, the baud rate generator is suspended

leaving the SDA line held low, and the START condi-

tion is complete.

15.2.7.1

WCOL STATUS FLAG

If the user writes the SSPBUF when an START

sequence is in progress, then WCOL is set and the

contents of the buffer are unchanged (the write doesn’t

occur).

Note: If at the beginning of START condition the

SDA and SCL pins are already sampled

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 I2C module is reset into its IDLE state.

Note: Because queueing of events is not

allowed, writing to the lower 5 bits of

SSPCON2 is disabled until the START

condition is complete.

FIGURE 15-23: FIRST START BIT TIMING

SDA

SCL

BRG

1st Bit

2nd Bit

BRG

SDA = 1,

At completion of start bit,

SCL = 1

Write to SSPBUF occurs here

BRG

automatic clear SSPCON2<0>

BRG

Write to SSPCON2<0> occurs here.

Set S bit (SSPSTAT<3>)

PIC17C752-08/P Datasheet(PDF) 144 Page - Microchip Technology

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