Microchip Technology MA160014 データシート
PIC18(L)F2X/4XK22
DS41412F-page 252
2010-2012 Microchip Technology Inc.
15.6.13
MULTI -MASTER COMMUNICATION,
BUS COLLISION AND BUS
ARBITRATION
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 I
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 I
2
C port to its Idle state (
).
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 I
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 I
2
C 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 I
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 I
2
C 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.
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.
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 I
detection of Start and Stop conditions allows the
determination of when the bus is free. Control of the I
2
C
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.
register, or the bus is Idle and the S and P bits are
cleared.
FIGURE 15-32:
BUS COLLISION TIMING FOR TRANSMIT AND ACKNOWLEDGE
SDAx
SCLx
BCLxIF
SDAx released
SDAx line pulled low
by another source
Sample SDAx. While SCLx is high,
data does not match what is driven
data does not match what is driven
Bus collision has occurred.
Set bus collision
interrupt (BCLxIF)
interrupt (BCLxIF)
by the master.
by master
Data changes
while SCLx = 0
while SCLx = 0