PIC16F872SLASHSP datasheet(69/160 Pages) MICROCHIP

69 / 160 page

Preliminary

DS30221A-page 69

PIC16F872

9.2.9

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 re-loaded 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.

9.2.9.5

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).

FIGURE 9-12: FIRST START BIT TIMING

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

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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