PIC18F242 datasheet(155/332 Pages) MICROCHIP

155 / 332 page

DS39564C-page 153

PIC18FXX2

15.4.8

I2C MASTER MODE START

CONDITION TIMING

To initiate a START condition, the user sets the START

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

and SCL pins are sampled high, the baud rate genera-

tor 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 (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. Follow-

ing 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 (SSPCON2<0>) will be automatically cleared

by hardware, the baud rate generator is suspended,

leaving the SDA line held low and the START condition

is complete.

15.4.8.1

WCOL Status Flag

If the user writes the SSPBUF when a START

sequence is in progress, the WCOL is set and the con-

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

occur).

FIGURE 15-19:

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 I2C module is reset into its

IDLE state.

Note:

Because

queueing

events

not

allowed, writing to the lower 5 bits of

SSPCON2 is disabled until the START

condition is complete.

SDA

SCL

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

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