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dsPIC30F1010/202X

DS70178C-page 158

Preliminary

2006 Microchip Technology Inc.

14.12.3

BAUD RATE GENERATOR

In I2C Master mode, the reload value for the BRG is

located in the I2CBRG register. When the BRG is

loaded with this value, the BRG counts down to ‘0’ and

stops until another reload has taken place. If clock

arbitration is taking place, for instance, the BRG is

reloaded when the SCL pin is sampled high.

As per the I2C standard, FSCK may be 100 kHz or

400 kHz. However, the user can specify any baud rate

up to 1 MHz. I2CBRG values of ‘0’ or ‘1’ are illegal.

EQUATION 14-1:

I2CBRG VALUE

14.12.4

CLOCK ARBITRATION

Clock arbitration occurs when the master deasserts the

SCL pin (SCL allowed to float high) during any receive,

transmit or Restart/Stop condition. When the SCL pin is

allowed to float high, the Baud Rate Generator is

suspended from counting until the SCL pin is actually

sampled high. When the SCL pin is sampled high, the

Baud Rate Generator is reloaded with the contents of

I2CBRG and begins counting. This ensures that the

SCL high time will always be at least one BRG rollover

count in the event that the clock is held low by an

external device.

14.12.5

MULTI-MASTER COMMUNICATION,

BUS COLLISION AND BUS

ARBITRATION

Multi-Master operation support is achieved by bus

arbitration. When the master outputs address/data bits

onto the SDA pin, arbitration takes place when the

master outputs a ‘1’ on SDA, by letting SDA float high

while another master asserts a ‘0’. When the SCL pin

floats high, data should be stable. If the expected data

on SDA is a ‘1’ and the data sampled on the SDA

pin = 0, then a bus collision has taken place. The

master will set the MI2CIF pulse and reset the master

portion of the I2C port to its Idle state.

If a transmit was in progress when the bus collision

occurred, the transmission is halted, the TBF flag is

cleared, the SDA and SCL lines are deasserted, and a

value can now be written to I2CTRN. When the user

services the I2C master event Interrupt Service

Routine, if the I2C bus is free (i.e., the P bit is set) the

user can resume communication by asserting a Start

condition.

If a Start, Restart, Stop or Acknowledge condition was

in progress when the bus collision occurred, the condi-

tion is aborted, the SDA and SCL lines are deasserted,

and the respective control bits in the I2CCON register

are cleared to ‘0’. When the user services the bus col-

lision Interrupt Service Routine, and if the I2C bus is

free, the user can resume communication by asserting

a Start condition.

The Master will continue to monitor the SDA and SCL

pins and, if a Stop condition occurs, the MI2CIF bit will

be set.

A write to the I2CTRN will start the transmission of data

at the first data bit, regardless of where the transmitter

left off when bus collision occurred.

In a Multi-Master environment, the interrupt generation

on the detection of Start and Stop conditions allows the

determination of when the bus is free. Control of the I2C

bus can be taken when the P bit is set in the I2CSTAT

cleared.

14.13 I2C Module Operation During CPU

Sleep and Idle Modes

14.13.1

I2C OPERATION DURING CPU

SLEEP MODE

When the device enters Sleep mode, all clock sources

to the module are shutdown and stay at logic ‘0’. If

Sleep occurs in the middle of a transmission, and the

state machine is partially into a transmission as the

clocks stop, then the transmission is aborted. Similarly,

if Sleep occurs in the middle of a reception, then the

reception is aborted.

14.13.2

I2C OPERATION DURING CPU IDLE

MODE

For the I2C, the I2CSIDL bit selects if the module will

stop on Idle or continue on Idle. If I2CSIDL = 0, the

module will continue operation on assertion of the Idle

mode. If I2CSIDL = 1, the module will stop on Idle.

I2CBRG

Fcy

Fscl

-----------

Fcy

1 111 111

---------------------------

–

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