OPTION_REG datasheet(169/222 Pages) MICROCHIP

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DS22331A-page 169

MCP19111

27.5.5

I2C MASTER MODE REPEATED

START CONDITION TIMING

A Repeated Start condition occurs when the RSEN bit

of the SSPCON2 register is programmed high and the

Master state machine is no longer active. When the

RSEN bit is set, the SCL pin is asserted low. When the

SCL pin is sampled low, the Baud Rate Generator is

loaded 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 deasserted

(brought high). When SCL is sampled high, the Baud

Rate Generator is reloaded and begins counting. SDA

and SCL must be sampled high for one TBRG. This

action is then followed by the assertion of the SDA pin

(SDA = 0) for one TBRG while SCL is high. SCL is

asserted low. Following this, the RSEN bit of 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 of the

SSPSTAT register will be set. The SSPIF bit will not be

set until the Baud Rate Generator has timed out.

FIGURE 27-19:

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’.

SDA

SCL

Repeated Start

Write to SSPCON2

Write to SSPBUF occurs here

At completion of Start bit,

hardware clears RSEN bit

1st bit

S bit set by hardware

TBRG

SDA = 1,

SCL (no change)

SCL = 1

occurs here

TBRG

and sets SSPIF

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