MCP19124 datasheet(161/236 Pages) MICROCHIP

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 2016 Microchip Technology Inc.

DS20005619A-page 161

MCP19124/5

28.3.5

START CONDITION

The I2C specification defines a Start condition as a

transition of SDA from a high state to a low state, while

SCL line is high. A Start condition is always generated

by the master and signifies the transition of the bus

from an Idle to an Active state. Figure 28-4 shows the

wave forms for Start and Stop conditions.

A bus collision can occur on a Start condition if the

module samples the SDA line low before asserting it

low. This does not conform to the I2C Specification that

states no bus collision can occur on a Start.

28.3.6

STOP CONDITION

A Stop condition is a transition of the SDA line from

low-to-high state while the SCL line is high.

28.3.7

RESTART CONDITION

A Restart is valid any time that a Stop is valid. A master

can issue a Restart if it wishes to hold the bus after

terminating the current transfer. A Restart has the same

effect on the slave that a Start would, resetting all slave

logic and preparing it to clock in an address. The master

may want to address the same or another slave.

In 10-bit Addressing Slave mode, a Restart is required

for the master to clock data out of the addressed

slave. Once a slave has been fully addressed,

matching both high and low address bytes, the master

can issue a Restart and the high address byte with the

R/W bit set. The slave logic will then hold the clock

and prepare to clock out data.

After a full match with R/W clear in 10-bit mode, a prior

match flag is set and maintained. Until a Stop

condition, a high address with R/W clear or a high

address match fails.

28.3.8

START/STOP CONDITION

INTERRUPT MASKING

The SCIE and PCIE bits in the SSPCON3 register can

enable the generation of an interrupt in Slave modes

that do not typically support this function. These bits

will have no effect on slave modes where interrupt on

Start and Stop detect are already enabled.

FIGURE 28-4:

I2C START AND STOP CONDITIONS

FIGURE 28-5:

I2C RESTART CONDITION

Note: At least one SCL low time must appear

before a Stop is valid. Therefore, if the SDA

line goes low then high again while the SCL

line stays high, only the Start condition is

detected.

SDA

SCL

Stop

Condition

Start

Condition

Change of

Data Allowed

Change of

Data Allowed

Restart

Condition

Change of

Data Allowed

Change of

Data Allowed

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