PIC17C752 datasheet(160/320 Pages) MICROCHIP

160 / 320 page

PIC17C75X

DS30264A-page 160

Preliminary

15.2.14 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 15-37).

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 ser-

vices the bus collision interrupt service routine, and if

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

tion by asserting a START condition.

If a START, RESTART, STOP, or Acknowledge condi-

tion 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 ser-

vices 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 taken when the P bit is set in the SSPSTAT

cleared.

FIGURE 15-37: 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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