PIC18F23K22 Datasheet, PDF (248/492 Pages) Microchip Technology – 28/40/44-Pin, Low-Power, High-Performance Microcontrollers with nanoWatt XLP Technology

PIC18(L)F2X/4XK22
15.6.13 MULTI -MASTER COMMUNICATION,
BUS COLLISION AND BUS
ARBITRATION
Multi-Master mode support is achieved by bus
arbitration. When the master outputs address/data bits
onto the SDAx pin, arbitration takes place when the
master outputs a ‘1’ on SDAx, by letting SDAx float high
and another master asserts a ‘0’. When the SCLx pin
floats high, data should be stable. If the expected data
on SDAx is a ‘1’ and the data sampled on the SDAx pin
is ‘0’, then a bus collision has taken place. The master
will set the Bus Collision Interrupt Flag, BCLxIF, and
reset the I²C port to its Idle state (Figure 15-31).
If a transmit was in progress when the bus collision
occurred, the transmission is halted, the BF flag is
cleared, the SDAx and SCLx lines are deasserted and
the SSPxBUF 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 SDAx and SCLx
lines are deasserted and the respective control bits in
the SSPxCON2 register are cleared. 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.
The master will continue to monitor the SDAx and SCLx
pins. If a Stop condition occurs, the SSPxIF bit will be set.
A write to the SSPxBUF 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
determination of when the bus is free. Control of the I²C
bus can be taken when the P bit is set in the SSPxSTAT
register, or the bus is Idle and the S and P bits are
cleared.
FIGURE 15-32:
BUS COLLISION TIMING FOR TRANSMIT AND ACKNOWLEDGE
Data changes
while SCLx = 0
SDAx line pulled low
by another source
SDAx released
by master
Sample SDAx. While SCLx is high,
data does not match what is driven
by the master.
Bus collision has occurred.
SDAx
SCLx
BCLxIF
Set bus collision
interrupt (BCLxIF)
DS41412B-page 248
Preliminary
 2010 Microchip Technology Inc.