18F8680 datasheet(225/496 Pages) MICROCHIP

225 / 496 page

 2004 Microchip Technology Inc.

DS30491C-page 223

PIC18F6585/8585/6680/8680

17.4.14

SLEEP OPERATION

While in Sleep mode, the I2C module can receive

addresses or data and when an address match or com-

plete byte transfer occurs, wake the processor from

Sleep (if the MSSP interrupt is enabled).

17.4.15

EFFECT OF A RESET

A Reset disables the MSSP module and terminates the

current transfer.

17.4.16

MULTI-MASTER MODE

In Multi-Master mode, the interrupt generation on the

detection of the Start and Stop conditions allows the

determination of when the bus is free. The Stop (P) and

Start (S) bits are cleared from a Reset or when the

MSSP module is disabled. Control of the I2C bus may

be taken when the P bit (SSPSTAT<4>) is set or the

bus is Idle, with both the S and P bits clear. When the

bus is busy, enabling the SSP interrupt will generate

the interrupt when the Stop condition occurs.

In multi-master operation, the SDA line must be moni-

tored for arbitration to see if the signal level is the

expected output level. This check is performed in

hardware with the result placed in the BCLIF bit.

The states where arbitration can be lost are:

• Address Transfer

• Data Transfer

• A Start Condition

• A Repeated Start Condition

• An Acknowledge Condition

17.4.17

MULTI -MASTER COMMUNICATION,

BUS COLLISION AND

BUS ARBITRATION

Multi-Master mode support is achieved by bus arbitra-

tion. 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 and

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 Bus Collision Interrupt Flag, BCLIF and reset the

I2C port to its Idle state (Figure 17-25).

If a transmit was in progress when the bus collision

occurred, the transmission is halted, the BF flag is

cleared, the SDA and SCL lines are deasserted and the

SSPBUF can be written to. When the user services the

bus collision Interrupt Service Routine and if the I2C

bus is free, the user can resume communication by

asserting a Start condition.

If a Start, Repeated Start, Stop, or Acknowledge condi-

tion was in progress when the bus collision occurred,

the condition is aborted, the SDA and SCL lines are

deasserted, and the respective control bits in the

SSPCON2 register are cleared. When the user ser-

vices the bus collision 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. If a Stop condition occurs, the SSPIF bit will be set.

A write to the SSPBUF will start the transmission of

data at the first data bit regardless of where the

transmitter left off when the bus collision occurred.

In Multi-Master mode, the interrupt generation on the

detection of Start and Stop conditions allows the determi-

nation of when the bus is free. Control of the I2C bus can

be taken when the P bit is set in the SSPSTAT register or

the bus is Idle and the S and P bits are cleared.

FIGURE 17-25:

BUS COLLISION TIMING FOR TRANSMIT AND ACKNOWLEDGE

SDA

SCL

BCLIF

SDA released

SDA line pulled low

by another source

Sample SDA. While SCL is high,

data doesn’t match what is driven

Bus collision has occurred.

Set bus collision

interrupt (BCLIF)

by the master.

by master

Data changes

while SCL = 0

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