PIC17C75X
15.2.14 MULTI -MASTER COMMUNICATION, BUS
COLLISION, AND BUS ARBITRATION
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.
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 Master will continue to monitor the SDA and SCL
pins, and if a STOP condition occurs, the SSPIF bit will
be set.
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the I C port to its IDLE state. (Figure 15-37).
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.
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
In multi-master mode, the interrupt generation on the
detection of start and stop conditions allows the deter-
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mination of when the bus is free. Control of the I C
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the I C bus is free, the user can resume communica-
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.
tion by asserting a START condition.
FIGURE 15-37: BUS COLLISION TIMING FOR TRANSMIT AND ACKNOWLEDGE
Sample SDA. While SCL is high
data doesn’t match what is driven
by the master.
SDA line pulled low
by another source
Data changes
while SCL = 0
Bus collision has occurred.
SDA released
by master
SDA
SCL
Set bus collision
interrupt.
BCLIF
DS30264A-page 160
Preliminary
1997 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
