PIC16F877-20SLASHP datasheet(83/218 Pages) MICROCHIP

83 / 218 page

 2001 Microchip Technology Inc.

DS30292C-page 81

PIC16F87X

9.2.10

I2C MASTER MODE REPEATED

START CONDITION TIMING

A Repeated START condition occurs when the RSEN

bit (SSPCON2<1>) is programmed high and the I2C

module is in the IDLE state. When the RSEN bit is set,

the SCL pin is asserted low. When the SCL pin is sam-

pled low, the baud rate generator is loaded with the

contents of SSPADD<6:0> and begins counting. The

SDA pin is released (brought high) for one baud rate

generator count (TBRG). When the baud rate generator

times out, if SDA is sampled high, the SCL pin will be

de-asserted (brought high). When SCL is sampled high

the baud rate generator is reloaded with the contents of

SSPADD<6:0> and begins counting. SDA and SCL

must be sampled high for one TBRG. This action is then

followed by assertion of the SDA pin (SDA is low) for

one TBRG, while SCL is high. Following this, the RSEN

bit in the SSPCON2 register will be automatically

cleared and the baud rate generator will not be

reloaded, leaving the SDA pin held low. As soon as a

START condition is detected on the SDA and SCL pins,

the S bit (SSPSTAT<3>) will be set. The SSPIF bit will

not be set until the baud rate generator has timed out.

Immediately following the SSPIF bit getting set, the

user may write the SSPBUF with the 7-bit address in

7-bit mode, or the default first address in 10-bit mode.

After the first eight bits are transmitted and an ACK is

received, the user may then transmit an additional eight

bits of address (10-bit mode), or eight bits of data (7-bit

mode).

9.2.10.1

WCOL Status Flag

If the user writes the SSPBUF when a Repeated

START sequence is in progress, then WCOL is set and

the contents of the buffer are unchanged (the write

doesn’t occur).

FIGURE 9-13:

REPEAT START CONDITION WAVEFORM

Note

1: If RSEN is programmed while any other

event is in progress, it will not take effect.

2: A bus collision during the Repeated

START condition occurs if:

•

SDA is sampled low when SCL

goes from low to high.

•

SCL goes low before SDA is

asserted low. This may indicate that

another master is attempting to

transmit a data "1".

Note:

Because

queueing

events

not

allowed, writing of the lower 5 bits of

SSPCON2 is disabled until the Repeated

START condition is complete.

SDA

SCL

Sr = Repeated START

Write to SSPCON2

Write to SSPBUF occurs here

Falling edge of ninth clock

End of Xmit

At completion of START bit,

hardware clears RSEN bit

1st bit

Set S (SSPSTAT<3>)

TBRG

SDA = 1,

SCL (no change)

SCL = 1

occurs here

TBRG

and sets SSPIF

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