PIC16F87X datasheet(98/200 Pages) MICROCHIP

98 / 200 page

PIC16F87X

DS30292A-page 98

9.2.18

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 TACKEN place. The master will

set the Bus Collision Interrupt Flag, BCLIF and reset

the I2C port to its IDLE state. (Figure 9-34).

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 de-asserted, 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

condition was in progress when the bus collision

occurred, the condition is aborted, the SDA and SCL

lines are de-asserted, and the respective control bits in

the SSPCON2 register are cleared. When the user

services the bus collision interrupt service routine, and

if the I2C bus is free, the user can resume communica-

tion by asserting a START condition.

The Master will continue to monitor the SDA and SCL

pins, and 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 trans-

mitter left off when bus collision occurred.

In multi-master mode, the interrupt generation on the

detection of start and stop conditions allows the deter-

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

can be TACKEN when the P bit is set in the SSPSTAT

cleared.

FIGURE 9-34: 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.

by the master.

by master

Data changes

while SCL = 0

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